(CBSNews) HONOLULU -- Authorities in Hawaii say one person is in critical condition after a civilian helicopter made a hard landing in the water near Pearl Harbor on Thursday.

The FAA said in a statement that a Bell 206 helicopter with five people aboard crashed into Pearl Harbor near the USS Arizona. All five were rescued.

A witness told CBS Honolulu affiliate KGMB-TV that the helicopter seemed to fall from the sky.

"My initial reaction was, 'This helicopter is kinda low flying.' It then hovered for a sec and then started to descend," witness Roy Gano said in an email to KGMB-TV. "It was not spinning out of control, but it was dropping at a good rate. It narrowly missed the rocky edge and turned to its side ... I saw people dive into the water to help."

A tourist from Australia said she was visiting Pearl Harbor when she heard a couple of loud bangs and realized a helicopter had crashed into the water.

Amber Moncrieff said boats seemed to come from everywhere. 

Officials say a 16-year-old passenger is in critical condition. Honolulu Emergency Services Department spokeswoman Shayne Enright says responders treated the teen and took him to a hospital after the hard landing on Thursday.

"We are told bystanders jumped in to help rescue these patients from the water," said Enright.

One of them was Chris Gardner, a tour guide with Keawe Adventures who was with a group of tourists at the visitor center when he heard the crash.

"I took off my shirt and dove in," he said, describing how he, a Navy sailor, a federal police officer and another man took turns diving to the submerged helicopter and trying to free a passenger with a knife. "He was strapped into his seat in the back of the aircraft."

They eventually freed the teenage passenger.

A 45-year-old woman and 50-year-old man were taken to the hospital in stable condition. Information wasn't immediately available about the two other people, including the pilot, treated and transported by the Federal Fire Department.

The helicopter crashed about 20 feet offshore, right next to the visitor center's lawn, said tourist Justice Winrich of Madison, Wisconsin. She watched as it "plopped down" into the water.

"I saw it like as it was coming in, and it looked pretty normal. It didn't look like it was shaking or anything," Winrich said. "It just started like getting really close this way and started going down." She thought it was strange that the helicopter was that close to people.

As it got closer to the water, she saw some dark smoke coming out of the back of the helicopter, and it started shaking slightly.

Winrich saw three people get out of the helicopter immediately and start swimming to shore.

"I was like, oh my God, I can't believe this just happened. It was crazy," she said. "You go on vacation and you never think you're going to see something like that."

Her father, Shawn Winrich, caught the crash on video. His footage shows the helicopter heading toward the water and then crashing down. The blades stop spinning as it turns over in the water.

Local author Allan Seiden was signing books at the visitor center when someone told him a helicopter crashed. He rushed over to where people were gathered, but by then the helicopter wasn't visible.

"I think it sunk instantly," he said.

Seiden watched as the helicopter's occupants -- including a man in a neck brace -- were carried away on stretchers. "People were very calm. ... You could tell everyone was very shocked," he said.

Federal records show the helicopter is registered to Jeffrey Gebhard of Kailua, Hawaii. He couldn't immediately be reached for comment.

The Navy said in a statement that the helicopter reportedly belongs to Genesis Aviation. The company website says it conducts helicopter tours of Oahu.

The Coast Guard received notification of the accident at 10:25 a.m.

FAA investigators are on their way and the NTSB has been notified, the FAA said in a statement earlier Thursday.

Joint Base Pearl Harbor-Hickam (JBPHH) Navy boats and Federal Fire (FFD) were among the first responders to the scene.