Tourists have described the moment they saw a helicopter "fall out of the sky" into the water at Pearl Harbor, Hawaii.
The crash happened Thursday near the USS Arizona Memorial, the U.S. Coast Guard said. Five people, including a family of four, were on board the single-engine helicopter.
"I heard a helicopter, I did not see it, I just heard it go into what we call auto rotation and I saw people running and screaming," tour guide Chris Gardner told ABC News' "Good Morning America" today. "I have credentials to run around to a secure area and just took off my shirt and dove in the water.
"Pearl Harbor is pretty murky. Luckily, the helicopter was only in about 10 feet of water. They were fortunate to have been flying with the doors off, which is a good thing so those passengers were accessible. Everybody had gotten out except, I guess he was a kid in the back, but I couldn't see much."
Tourist Shawn Winrich says he'd just gotten off the boat to see the memorial and "was shooting some still pictures of the harbor and happened to have my phone aimed in that direction and noticed the helicopter flying awkwardly low and essentially coming straight for us."
"I could see a helicopter really close because I thought it would be great video," Winrich said. "All of a sudden, it essentially just fell out of the sky and crash-landed in the water.
"My natural instincts kicked in and I realized that there were people in there and we need to get over there quickly and, hopefully, get them out of there.
"It was coming in pretty close but then as soon as it started dropping it was fairly obvious that it was going to crash. At that instant, I did have a momentary fear for safety of myself and others around me with rotating blades."
The National Transportation Safety Board will investigate the crash.
Three members of the family on board, including a 15-year-old boy, were taken to Pali Momi Medical Center in Aiea, Hawaii, a hospital spokesman said. The boy was listed in critical condition and the two others were in stable condition.
The fourth member of the family was treated at another hospital and released, the Pali Momi Medical Center spokesman said.
It's unclear whether the remaining passenger was injured.
Gardner was quick to add he wasn't a hero: "This is what we do. We run to a fight, it's just instinct. Any of my friends would have done the same thing."
"Here in Hawaii we don't run from problems, especially in the water. Anybody else would have done the same thing and there was multiple people that jumped in the water at the same time. It's just the way we do it here."
Fellow tourist Amber Moncrieff said, "I heard a couple very loud bangs. We were obviously concerned about what that was and I saw one of the tour guides - an elderly guy - jump a fence so I knew that things were not good.
"One of our group then went around the side and realized a helicopter had crashed into the water."