JOPLIN, Mo. >> Emergency crews drilled through concrete at a ruined Home Depot, making peepholes in the rubble in hopes of finding lost shoppers and employees. A dog clambered through the shattered remains of a house, sniffing for any sign of the woman and infant who lived there.

Across devastated Joplin, searchers moved from one enormous debris pile to another Tuesday, racing to respond to any report of a possible survivor.

The human toll rose to at least 122 dead and 750 people hurt. But just nine had been pulled alive from the aftermath. Searchers fought the clock because anybody still alive after the deadliest single tornado in 60 years was losing precious strength two days after the disaster. And another round of storms was closing in.

For Milissa Burns, hope was fading that her 16-month-old grandson, whose parents were both hospitalized after the tornado hit their home, would be found.

She showed up Tuesday at a demolished dental office near the child’s home to watch a search team. At one point, a dog identified possible human remains, prompting eight searchers to dig frantically, but they came away with nothing. Burns was weary but composed. Her daughter — the boy’s aunt — sobbed next to her.

“We’ve already checked out the morgue,” Burns said. “I’ve called 911 a million times. I’ve done everything I can do. He was so light and little. He could be anywhere.”

Also Tuesday, the National Weather Service announced that the twister that crippled Joplin was an EF-5, the strongest rating assigned to tornadoes, with winds of more than 200 mph. Scientists said it appeared to be a rare “multivortex” tornado, with two or more small and intense centers of rotation orbiting the larger funnel.

It was the deadliest single twister since the weather service began keeping official records in 1950 and the eighth-deadliest in U.S. history.

A short time later, severe thunderstorms spawned a tornado that killed two people during the evening rush hour in suburban Oklahoma City.

Another top job was testing the city’s tornado sirens to make sure they were operable ahead of another round of potentially violent weather starting Tuesday evening and expected to last into Wednesday in some places. Emergency officials warned jittery residents well in advance of the test.

David Imy, a meteorologist at the federal government’s Storm Prediction Center in Norman, Okla., said conditions were ripe for severe thunderstorms, including tornadoes, in parts of Kansas, Missouri, Arkansas, Texas, Kentucky and Tennessee, as well as nearly all of Oklahoma.

Throughout the search efforts, new reports emerged of clusters of victims: 11 people dead in a nursing home, three bodies found in an Elks Lodge.

The tornado tossed three vehicles into the Greenbriar nursing home and left nothing more than a 10-foot section of an interior wall standing. On the night of the twister, the Joplin Elks lodge had been scheduled to host its weekly bingo game.

“If that had been two hours later, there could have been 40 or 50 people in there,” said Chris Moreno, a hospital lab technician coordinating an outdoor triage center.

Jasper County Emergency Director Keith Stammer said the scope of the destruction was making it difficult to account for people affected by the storm. He suggested that many survivors, with nowhere to go, left Joplin for Kansas, Arkansas, Oklahoma or other parts of Missouri.

“There’s a lot of confusion, a lot of inability for folks to communicate,” he said.

Authorities also announced a curfew from 9 p.m. to 6 a.m., with only residents and emergency workers allowed inside the disaster zone.

People in the Joplin area and beyond have turned to online social networks to find family members missing since the tornado or to learn about the plight of survivors.

Multiple Facebook pages created since the tornado are filled with requests for information about specific people who have not been heard from since Sunday. Some pages include photos of the missing. Other posts share the news about Joplin residents who are alive and well.

Several social-networking efforts specifically focused on finding information about Will Norton, a teenager who vanished on his way home from his high school graduation ceremony. More than 10,000 people have supported the “Help Find Will Norton” community page on Facebook, and Twitter users were tweeting heavily about the missing teen.

Family members told The Associated Press that Norton and his father were still on the road when the storm hit. Mark Norton urged his son to pull over, but the teen’s Hummer H3 flipped several times, throwing the young man from the vehicle, likely through the sunroof.

The elder Norton was hospitalized.

Confusion clouded the number of dead and survivors. A spokesman for Gov. Jay Nixon said 117 bodies had been found, along with 17 survivors pulled from the rubble. The fire chief said he only knew of 116 bodies and seven survivors.

From the air, the difficulty of the search was apparent.

The tornado damage was “like taking a mower through tall grass. That’s what it looks like,” said state Sen. Ron Richard of Joplin, who flew over the area with Nixon and Sen. Claire McCaskill. He described the devastation as “down to the ground.”

The Home Depot was identifiable only by the prevalence of the store’s signature orange color in the corrugated roofing and metal framing that looked almost as if it had been melted.

Jackhammers pounded against heavy concrete slabs that once held up the store. Crews were desperate to punch through so dogs could sniff for any scent of people below. A day earlier, rescuers found one person alive in the store’s wreckage but also recovered seven bodies under the concrete.

In the waiting room of Freeman Hospital, Debbie McMurry and Dan Perry sat waiting for any news about their 76-year-old mother, Mary Joyce Perry. She was chatting online Sunday afternoon with McMurry when the lights began to flicker in her home, two streets away from the now-destroyed Joplin High School, McMurry said Tuesday.

When McMurry arrived that night to check on her mother, Perry’s home had been flattened. Someone had left a cardboard sign near the wreckage: “Joyce Hospital?” A neighbor had seen someone carry Perry out of the house and take her away.

Dozens of relatives and friends have called hospitals throughout the region, and Dan Perry’s son was trying to get into a makeshift morgue for tornado victims to look for her body. Meanwhile, her family members continued to wait at Freeman, where more than 500 storm victims have been treated and 11 have died.

“Who knows?” Dan Perry said Tuesday. “She could be anywhere.”

Some searches that looked bleak ended in joy.

Near the hospital, in what was once a neighborhood overlooking a park, John DeGraff and a friend were picking through the remains of DeGraff’s home when his neighbor, Larry Allen, walked up. Tears welled in DeGraff’s eyes and he hurried to embrace Allen.

“Larry, where you been, man?” DeGraff asked. “We’ve been looking for you. We’ve been digging through here since Sunday.”

“God bless you,” Allen said. “Have you seen the cats?” DeGraff had not.

Allen said he tried to get to the basement when the tornado hit, but got his foot caught on a step heading downstairs and waited it out there. Good thing: The entire upstairs fell into the basement.

Allen, who lives alone, was able to walk out and stayed with friends before returning Tuesday to see what was left of his house.

Like DeGraff’s, it was destroyed. DeGraff recovered a few old record albums. He smiled when he found a small football, a memento from his days on the 1980 team at Joplin High School. As DeGraff yelled to other neighbors that Allen was alive and well, another neighbor brought him pictures and other personal items she found for him.

“I didn’t know people cared about me so much,” Allen said.

About a mile to the east, Robin Ross sobbed as she held her 21-year-old son, John.

For 36 hours, Ross hadn’t heard from her son, who doesn’t have a cellphone. The morning after the storm, she raced the 12 miles from her Carl Junction home to Joplin and found the home where he was living in ruins. She couldn’t reach his friends, and drove the neighborhood in search of him.

Ross said neighbors told her they had seen her son after the storm hit, but didn’t know his location. Finally, on Tuesday, a friend was able to find the young man and direct his mother to him. He had climbed out of the wreckage and started helping with cleanup.

“I’ve been crying since Sunday,” she said. “And it wasn’t just for my family. It was for everyone.”