Updated

The National Transportation Safety Board says three of nine presumed victims of a helicopter-plane collision over the Hudson River have been recovered.

NTSB chair Deborah Hersman says the recovery operations have been called off and will resume Sunday morning, due to compromising tides and low visibility.

The accident happened just after noon between Manhattan and Hoboken, N.J. when a small private plane collided with a sightseeing helicopter over the Hudson River, leaving debris scattered in the water and on the New Jersey shoreline, sending witnesses ducking for cover.

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A helicopter pilot refueling on the ground at the heliport for Liberty Tours, which operated the doomed sightseeing craft, saw the plane approaching the helicopter and tried to radio an alert to the pilots, police Commissioner Raymond Kelly said. The warning wasn't heard or didn't happen in time.

"He radioed the accident helicopter and told him, 'One-lima-hotel, you have a fixed wing behind you,"' Hersman said. "There was no response."

The sight-seeing helicopter was carrying five Italian tourists and a pilot, and the plane was carrying a pilot and two passengers, one of whom is believed to have been a child, New York City Mayor Michael Bloomberg said at an afternoon press conference.

"This is not going to have a happy ending," the mayor said. "This has changed from a rescue to a recovery mission."

"If anybody had survived, we would have been there," said Bloomberg. "Sadly, it appears to us at this point that this was not survivable."

Both craft are under water and may have sunk to a depth of 30 feet, he told reporters. Though it was a crystal-clear summer day in New York, visibility is only about two feet in the water, making the recovery process extremely difficult, according to the mayor.

"We have found one piece of wreckage. This is a dangerous area when the currents are running," he said, adding that divers were not to put their lives at risk in a recovery mission unlikely to bring back any survivors.

The plane, a Piper PA-32, took off from Teterboro Airport in New Jersey, and the helicopter was a Eurocopter AS 350 owned by Liberty Tours, a sightseeing and charter company, the Federal Aviation Administration said.

FAA spokesman Jim Peters said the plane was headed to Ocean City, N.J., with three people aboard and that it was believed there were five passengers and one crew member on the helicopter.

Authorities were told the plane crashed "into the backside of the helicopter," Bloomberg said, warning reporters that the actual facts of the accident won't be known for months.

People who saw the accident and its aftermath described the two aircraft colliding not far from the Hoboken shoreline, and said the impact sheared off the plane's wing.

"There was a loud pop, almost like a car backfire," said Buzz Nahas, who saw the crash from Hoboken. "The helicopter dropped like a rock."

Katie Tanski of Hoboken heard the noise of the collision, looked up and saw chaos in the air.

"We saw the helicopter propellers fly all over," she said. Some pieces of the wreckage fell on land, sending Tanski and others scurrying for cover.

Governor Jon S. Corzine called the crash a "devastating tragedy" and that the Hoboken Police, New Jersey State Police, the Port Authority of New York and New Jersey and the New York City Police Department were all in the recovery efforts of this horrible crash.

"All of us in this region also need to take a long and serious look at the circumstances surrounding this crash to ensure that significant air traffic over the Hudson doesn't come at the risk of the safety of New Jersey families who live along the riverfront," said Corzine.

Seven months ago, the same river was the scene of a spectacular aircraft accident. In January, a US Airways flight taking off from LaGuardia Airport slammed into a flock of birds and lost power in both engines. The plane crash-landed in the Hudson River, and all 155 people on board were pulled to safety.

Liberty Tours runs sightseeing excursions around the Statue of Liberty, Ellis Island and Manhattan at costs ranging from $130 to about $1,000.

A person who answered the phone at a Liberty Tours office declined to comment on the accident, but said the company would be releasing a statement.

Two years ago, a Liberty helicopter fell 500 feet from the sky during a sightseeing trip. The pilot was credited with safely landing the chopper in the same river and helping evacuate her seven passengers.

In 1997, a rotor on one of its sightseeing helicopters clipped a Manhattan building, forcing an emergency landing. No one was hurt

The Aircraft Owners and Pilots Association reports there have been 70 midair collisions involving 140 aircraft in the United States over the last 10 years. There were fatalities aboard 83 of those aircraft.

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The Associated Press contributed to this report.