A passenger plane carrying at least 29 people plunged into the sea off Gabon yesterday and 10 people were rescued, officials from the aircraft's operator Gabon Express said.

A French army helicopter helped rescue the 10 who were taken to a hospital in the central African country's capital Libreville. Divers were still trying to reach others trapped inside the plane hundreds of metres away from the coast.

Local fishermen were also helping in the rescue effort. "Rescuers have managed to get into the aircraft and we are waiting to see what the outcome is," an official from Gabon's transport ministry told local television.

The plane was travelling from Libreville to Franceville in the southeast of the former French colony, via Port-Gentil, the economic capital.

One airline official and a Western diplomat said that 26 passengers, including Africans and Westerners, and three crew members were aboard the plane when it crashed.

"There seem to have been 26 registered passengers plus a pilot, co-pilot and a steward. Of those so far we know that 10 have survived and are in hospital," the diplomat told Reuters by telephone.

"The tail is sticking up out of the water. It clearly landed in such a way that some people had time to get out before it was submerged," he added.