A passenger plane carrying at least 29 people plunged into shallow waters just off the coast of Gabon on Tuesday killing many of those on board, officials from the aircraft's operator said.

A French army helicopter helped rescue 10 people, who were taken to hospital in the central African country's capital Libreville.

Divers tried to reach others trapped inside the Gabon Express plane, just hundreds of metres (yards) from the shore. 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," a Transport Ministry official 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.

A local radio station said it had developed engine trouble soon after taking off.

Lebanon's ambassador in Gabon, Gharamy Ayoub, said two Lebanese nationals were on board when it crashed.

"One has died and the other was hospitalized with minor injuries. He is in good health," Ayoub said.

One Gabon Express official and a Western diplomat said 26 registered passengers, including Africans and Westerners, and three crew were aboard the plane when it crashed.

"Of those, so far we know that 10 have survived and are in hospital," the diplomat said. "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."

Local residents had flocked to the beach to look at the crash scene, blocking roads in the city, witnesses said.

The plane's crew had noticed a problem with the engine shortly after take-off and had been trying to land again at the airport, Libreville-based Africa No1 radio said.

Africa's poorly maintained airlines are prone to disaster. Three planes crashed into the ground shortly after takeoff around the continent last year.

Oil-rich Gabon, home to 1.3 million people, is one of Africa's wealthiest countries with per capita income of USD$4,700 a year according to central bank figures -- many times the average for sub-Saharan Africa.

(Reuters)