A sea search is under way for some 20 missing passengers after a light aircraft came down in Gabon. Eight passengers swam to shore and were airlifted to hospital after the privately-owned plane crashed off a beach near the capital Libreville. The plane was flying from Libreville to Franceville in the southeast of the former French colony when it crashed shortly after take off. French troops stationed in Gabon are leading the rescue effort. **Floating wreckage*** The plane came down in the Gulf of Guinea, about 100 metres from the shore, shortly after taking off at 0915 local time (0815 GMT), one official said. The two-engine propeller plane was believed to belong to Gabon Express, a private company in the West African nation. Thousands of onlookers were reported to have thronged the beach, not far from the Leon Mba international airport, to watch the rescue effort. "Eight boats are surrounding the floating wreckage trying to retrieve bodies," said BBC's Daniel Mboungou-Mayengue speaking from the scene. "A bulldozer is on the beach attempting to winch the wreck to shore, with difficulty," he said. Minister of Transport Paulette Missambo said at a news conference that three crew members and 26 passengers were on board. The Associated Press quoted an official of the company as saying the passenger roster indicated foreigners were on board. Mrs Missamboe did not know officially what had caused the accident. But a staff member of Asecna - the Agency for Air Navigation Safety in Africa and Madagascar - told our reporter that the pilot called the airport tower to say he had a problem with one of the propeller's blades. He was making a U-turn to attempt an emergency landing when the plane crashed, the source said.