A single-engine Beechcraft Sundowner reportedly experienced engine trouble while inbound to Honolulu airport this morning and made an emergency water landing just off Makaha Beach.

The two people on board, a 56-year-old man and a 52-year-old woman, both of Hawaii, sustained minor injuries.

Both were spotted wearing flotation-vests and clinging to a wing of the plane shortly before it sank into a surfing area known as Charlie’s Reef, said Shayne Enright, a spokeswoman for the city Emergency Services Department.

Two lifeguards spotted the aircraft’s tail jutting from the reef’s waters at about 11:20 a.m., and swam to the scene — about 50 yards from shore. Shortly thereafter, a “Good Samaritan” Jet Ski operator arrived at the scene and carried all four to Makaha Beach Park, Enright said.

Responding paramedics treated the man and woman for abrasions and transported them to a hospital in stable condition.

Ocean Safety personnel are now monitoring the crash area, checking for debris and have installed equipment to address potential oil spill.

There were no swimmers in the area at the time of the crash, Enright said.

At least a few fishermen were in nearby waters, however.

Robby Oliveros, 18, and his cousin, Austin Inabata, 21, were fishing off the shore nearby when they were warned that an airplane was about to crash.

“All of a sudden, a fisherman right next to us said, ‘Head’s up. There’s a plane coming.’ And we looked up,” Oliveros said. “Then the plane was coming toward us and it took a left and it headed toward Makaha Beach. It just started gliding down into the water. It just nearly missed shore.”

Oliveros posted a photo on Twitter showing only the tail of the aircraft sticking out of the water.

“It actually came in nice and slow and looked like nothing was wrong with the plane,” Oliveros said. “From what I witnessed, it just looked like it ran out of gas or something, or maybe an engine failure.”

The plane was “quiet” as it descended and “just made a big splash. The plane was just floating and then the guy got out and he was standing on his plane,” Oliveros said.

The plane sank in water that Oliveros estimated is 20 to 30 feet deep.

The Federal Aviation Administration and National Transportation Safety Board are investigating.

Enright said city officials were told that the couple on the plane are from Oahu. A state Department of Transportation spokesman said the flight originated out of Lihue.

The crash was the second involving a small plane in Hawaii today. Earlier this morning, a skydiving tour plane crashed near Port Allen Airport on Kauai, killing the five people on board.