A passenger plane plunged into the sea near Tahiti moments after take-off from a nearby island and all 20 people on board are feared dead, including two Americans, officials in French Polynesia said.

Two European Union officials and a number of local officials were also on board the Air Moorea turboprop aircraft when it went down.

Witnesses said they saw it ploughing into the waves soon after taking off from Moorea's Tamae airport at midday (2200 GMT on August 9) for the 17-kilometre (10-mile) flight to the nearby South Pacific island of Tahiti.

"The plane seemed to have difficulty gaining altitude," an airport employee who saw the crash said.

"Then it plunged and you could hear the noise of the explosion."

So far 16 bodies have been recovered from the Twin Otter plane and divers are searching for the rest, according to officials in Papeete, capital of the French overseas territory.

Of the 19 passengers, five were foreigners -- three tourists including two US citizens plus two EU development fund officials. Five members of the French Polynesian environment ministry were also on board.

The first rescue workers on the scene found nothing but debris and floating bodies.

"The bodies were coming up slowly, one after the other," said one of the rescuers, adding "it seems that the cabin disintegrated upon impact as all the passengers are still buckled in."

Two helicopters were being used to look for the remaining passengers, said Jacques Witkowski, the secretary general of French Polynesia's High Council.

The cause of the crash was not immediately clear, but an investigation has been launched.

The bodies of the victims have been moved to a makeshift morgue in a nearby village where identification was underway.

The crash was the first for an Air Moorea aircraft, according to officials. The plane, which the company had operated for one year, was last inspected on July 18.

French Polynesia's president Gaston Tong Sang immediately flew to the scene of the crash, where he spoke of the "cruel tragedy for Polynesia."

A team of psychologists has been mobilised to help families of the victims, as well as a telephone hotline for information, according to the government's website.

France's top official for overseas territories, Interior Minister Michele Alliot-Marie, voiced her "sincere condolences to all the families touched by this tragedy."

She paid tribute to the rescuers and vowed that families and investigators would receive all the support they need.

Alliot-Marie ordered Christian Estrosi, the junior minister responsible for French overseas territories, to travel to the islands as soon as possible.