Emergency workers look for debris on the Hudson River after Saturday's accident. A small plane and a sightseeing helicopter carrying Italian tourists collided over the Hudson River between New York City and Hoboken, N.J., on Saturday, killing all nine people aboard the two aircraft.

"Sadly, it appears to us at this point that this was probably not survivable from virtually the instant both aircraft went into the water," New York Mayor Michael Bloomberg told reporters a few hours after the collision.

Five tourists and the pilot were aboard the helicopter, which had lifted off from the West 30th Street Heliport on Manhattan's west side. A pilot and two passengers, one of them a child, were on the plane, a Piper PA-32 that had taken off from Teterboro Airport in New Jersey.

The crash happened just after noon and was witnessed by thousands of people enjoying a clear summer day from the New York and New Jersey sides of the river.

By Saturday evening, three bodies had been recovered from the water. The National Transportation Safety Board, which is investigating, said diving recovery operations had been called off until Sunday morning.

Initial reports from the U.S. Coast Guard that one person had been rescued turned out to be incorrect.

Witnesses said both aircraft were heading south when they collided on the New Jersey side of the river near an area called Pier 40.

Pilot on ground radioed warning

Another helicopter pilot on the ground at the heliport saw the plane approaching the helicopter and tried to radio an alert to the pilots, police commissioner Raymond Kelly said. The warning apparently wasn't heard or didn't come in time.

Buzz Nahas, who saw the crash from the shore in Hoboken, said there was a loud pop, like a car backfiring.

The helicopter "dropped like a rock," he said, and the plane lost a wing.

Jose Granado told CBC News he saw the crash as he was standing on the pier. He said the plane appeared to be flying under the helicopter when it made contact.

"The helicopter started spinning out of control," he said.

Some pieces of the wreckage fell on land along the Hoboken shoreline, sending witnesses running for cover.

Granado said he, too, began to run from the scene.

"I turned back and probably within a minute to a minute and a half there were emergency vehicles surrounding the crash area," he said.

The helicopter was a Eurocopter AS 350 owned by Liberty Tours, a sightseeing and charter company, FAA officials said.

With files from The Associated Press