NEW YORK: Nine people were believed dead Sunday after a helicopter carrying Italian tourists crashed mid-air with a light airplane over New York's Hudson River.

"Three victims have been recovered," said Debbie Hersman, head of the National Transportation Safety Board, at a late Saturday press conference, adding that search operations had been suspended for the night.

Media reports said the bodies of two adults and one child had been pulled from the Hudson, hours after the helicopter carrying five tourists and a pilot collided with an airplane in full view of horrified residents.

Hersman said she could not confirm the identities of the three bodies, or which aircraft they had been aboard.

Earlier in the day, New York Mayor Michael Bloomberg told a press conference that what had started as a rescue operation was being converted into a recovery operation, saying the incident was "not survivable."

"This is not going to have a happy ending," he said.

Hersman said divers had located the wreckage of the helicopter and were using sonar equipment to search for the plane before they shut down operations overnight.

"Once that wreckage is pulled up, they will try to do it tomorrow, depending on the current and the circumstances and the conditions... it will be pulled up and taken to a secure location for further examination," she said.

The search for the wreckage was made more difficult by the low visibility of only about one metre (three feet) at the bottom of the river, authorities pointed out.

The Eurocopter AS350 was carrying five Italian tourists and a pilot. Two passengers, including one child, plus a pilot were aboard the single-propeller Piper PA32 plane.

The collision took place just after noon (1600 GMT) on a hot summer day when river-front streets were crowded with locals and tourists.

Witnesses described the two aircraft plummeting into the river between Manhattan and New Jersey.

"It hit the water like a stone," a woman told NY1. "I saw a piece of metal, I saw a helicopter, the helicopter went down, and that was it. I heard no noise, and no smoke or fire."

Some witnesses said the accident had been almost noiseless, but others reported hearing either the collision or impact against the river.

"We heard a really loud crash which sounded like lightning or thunder," another woman said. "They were both falling from the sky."

Witnesses also spoke of seeing debris -- either part of the plane's wing or fragment of the chopper's rotor -- fluttering down.

New York state Governor David Paterson offered the bereaved his condolences.

"What began as a beautiful day with blue skies has turned into a day of darkness for those who lost someone they love today," he said.

Immediately after the accident, rescue craft rushed to the scene. However, it soon became clear that they had little to do.

Officials said the light plane had taken off from Teterboro Airport in New Jersey, while the helicopter belonged to a company providing flights for tourists.

Their collision took place in a densely crowded air corridor used by commercial flights, private pilots and tourist helicopters.

New Jersey Governor Jon Corzine called the accident "devastating" and said that safety measures needed checking.

"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," he said.

This January an Airbus jet operated by US Airways lost power over New York but the pilot made a successful splash landing in the Hudson, just off Manhattan, with no loss of life.

The accident happened after the airliner hit a flock of wild geese, resulting in both engines being disabled.