Four people escaped serious injury when a helicopter crashed into the sea off Lake Tashmoo about 2:30 p.m. Sunday.

Police said engine failure was the cause of the crash.

Several private fishing and pleasure boats were on the scene, about 1,000 yards off Tashmoo, within minutes and threw life jackets to the passengers clinging to the upturned chopper.

The occupants were then able to swim the short distance to the boats. It is believed three boats ferried them to shore. All were checked at the Martha’s Vineyard Hospital and quickly released.

“They seemed pretty shaken up, but none was injured, I think,” said an eyewitness, Sid Smith, whose boat was second at the scene.

“I saw it happen. It looked like the helicopter was coming down to land on the water. The I realized it didn’t have any pontoons.

“It touched the water with the rotor still spinning, then rolled to the right. The blades caught the water and flipped the whole thing upside down. But it floated.

“The people climbed out okay, but they didn’t want to swim to the boats,” Mr. Smith said.

He said the larger boats could not approach too close to the chopper because of concerns about striking the blades.

“A couple of smaller open fishing boats got in close and got them,” he said. Vineyard Haven harbor master Jay Wilbur later got a line on the crashed aircraft and towed it to shallow water.

“There didn’t appear to be much damage to the chopper, except it’s waterlogged,” said Mr. Wilbur.

A spokesman for the state police said the helicopter would now be towed again, probably to the Lake street boat ramp, and pulled from the water.

Then it will be taken to the airport for inspection by the Federal Aviation Administration, to determine more precisely what went wrong.