New York, Aug 9 (DPA): A mid-air collision of a New York sightseeing helicopter and a single-engine plane killed nine people, including five Italian tourists, triggering a major search on the Hudson River between New York City and Hoboken, New Jersey.

By twilight Saturday, divers had recovered three bodies, including that of a child, and planned to resume their search Sunday at 1100 GMT, the chief accident investigator told reporters.

Deborah Hersman of the National Transportation Safety Board (NTSB) said divers had located the helicopter operated by Liberty sightseeing tours that had been carrying the five Italian tourists and a pilot.

They were still searching for the single-engine Piper Saratoga that was carrying the pilot, an adult and a child. The search was difficult in the murky waters of the Hudson River, where Hersman said visibility was less than one metre.

The helicopter took off about noon from a heliport on 30th Street for the sightseeing tour as the Piper was making its way south along the Hudson from the Teterboro airport outside New York City toward Ocean City, New Jersey.

Hersman said another Liberty helicopter pilot was refueling, saw the approaching accident and tried to warn the pilot.

"He saw the single-engine aircraft approaching behind the helicopter, and told them (on radio) 'One Lima Hotel you have a fixed wing behind you'," Hersman said.

"He saw the right wing of the plane contact the helicopter. The right wing fell. Then both aircraft," Hersman said.

The debris fell into the Hudson River somewhat north of the Statue of Liberty in New York Harbour.

New York Mayor Michael Bloomberg said there was "some evidence from eyewitnesses that one of the wings of the airplane was ...possibly severed by the rotors of the helicopter".

The mayor said special community affairs officials had been sent to help the families of the Italian tourists.

"I gather they don't speak English," he said, adding the officials would "help the families get through this difficult period".

Hersman said investigators do not expect to retrieve black box recorders, which are not required on such small aircraft. But they could get some data from air traffic control radar and equipment on board the aircraft, depending on the damage.

"I have not been made aware of any distress calls that were made," Hersman said.

Bloomberg noted that small aircraft and helicopters have flight corridors over the Hudson and East Rivers. While there is no legal requirement for radio contact and visual flight rules were in effect, he said it was common practice for pilots to use a radio frequency identified on all maps to make each other aware of their positions.

"It is a crowded busy area, and pilots who fly there are well trained and have practice," he said.

It was not clear if the pilots were in radio contact with each other.