More than 200 people were stung by box jellyfish at Waikiki and Ala Moana beaches over the last two days, and lifeguards are urging people to stay out of South Shore waters today to avoid the painful welts.

The creatures are nearly invisible in the water, and their sting can be lethal to people who are allergic, if not promptly treated. Since the jellyfish influx began Wednesday, three people were sent to the hospital for anaphylactic shock after being stung, said Capt. Paul Merino, supervisor of Ocean Safety and Lifeguard Services for the South Shore.

Yesterday, 127 stings were reported, mostly at Waikiki Beach, and a total of more than 100 people were stung the day before at Waikiki and Ala Moana, Merino said.

"The whole South Shore is affected," he said yesterday. "They’re inundating the beaches. The lifeguards are just overwhelmed.

"A lot of people don’t know they are allergic until they get bit, and their respiratory system slows and we have to call the ambulance."

The jellyfish influx is expected to last through New Year’s Day and begin to fade on Sunday, he said. Lifeguards posted warning signs beginning Wednesday, but the temptation to hit the water was too strong for many beachgoers.

"Being that it’s such a nice day, people aren’t heeding the warnings," Merino said yesterday. "It’s a perfect storm. It was rainy all week, and now it’s sunny and beautiful today and jellyfish are on the beach."

Box jellyfish typically measure 1 to 2 inches long, with tentacles that stretch about a foot long. Even those that are lying on the sand can be toxic and should not be touched. Beachgoers who are stung can use an ice pack or immerse the wound in warm water to relieve the pain, Merino said.

In Hawaii, box jellyfish tend to come near the shore to spawn about 10 days after the full moon. Beachgoers are advised to inquire with lifeguards about any potential dangers, from jellyfish to ocean currents.