(Adds French help, paragraphs 7-8; Equatorial Guinea politicians on board, 12)

By Tansa Musa

YAOUNDE, May 5 (Reuters) - Heavy rain and thick forest hampered efforts to find a Kenya Airways passenger plane which crashed on Saturday shortly after takeoff in southern Cameroon with 114 people on board, officials said.

Military and civil aviation helicopters scoured a wide zone in the central African country between Kribi on the Atlantic coast and Ngomedzap, south of the capital Yaounde, but the remote location and poor weather did little to help.

"We've even sent boys out on motorcycles along main routes in the region to see whether they can see any trace of the plane crash," Jean-Francois Nzenang, senior administrative officer for the region around Kribi, told Reuters by telephone.

"Some of the area is inaccessible by road and there are no telecommunications signals."

State radio earlier reported the plane -- which was carrying passengers from more than 20 countries -- had crashed near Nieté, north of the border with Equatorial Guinea, after taking off from Cameroon's second city of Douala.

But after no wreckage was immediately found, the search with radar-equipped helicopters shifted to another area southwest of the capital -- between the towns of Lolodorf and Ebolowa -- where inhabitants said they had heard a loud explosion.

France sent help from a military base in neighbouring Gabon.

"A French Super Puma helicopter attached to the Libreville marine battalion has been sent to Cameroon to help locate the crash site. It is currently in action," the French embassy in Cameroon said in a statement.

Kenya Airways Group Managing Director Titus Naikuni told a news conference in Nairobi that the authorities in Cameroon had picked up a distress signal, automatically generated by a machine, from the area where the plane went missing.

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Kenya Airways said the 737-800 airliner, which began its journey in Ivory Coast's main city Abidjan and stopped over in Cameroon, was carrying 105 passengers and nine crew.

The airline said there were Cameroonians, Indians, South Africans, Chinese, Nigerians, Ivorians, Britons and an American among the passengers. The crew were all Kenyans.

Equatorial Guinea's government said two members of its parliament were on board the plane. They were travelling to attend a meeting of the Pan-African parliament in South Africa.

Kenya Airways said the Douala control tower had received the last message from the aircraft right after takeoff. The plane had been due to land in Nairobi at 6:15 a.m. (0315 GMT).

Kenyan Transport Minister Chirau Ali Mwakwere said the U.S. government was assisting in the search with satellite images taken over the expected flight path.

Worried relatives, several in tears, came to seek information at Nairobi's Jomo Kenyatta International Airport. One woman passed through the lobby wailing, mobbed by journalists before she was ushered away by security staff.

Kenya Airways, one of Africa's few profitable carriers, set up a crisis centre to monitor events and a passenger information centre at a hotel in Nairobi.

The carrier has a good safety record on a continent where air accidents are above the world average. The plane was 6-months-old and had no history of problems, Naikuni said.

On Jan. 30, 2000, a Kenya Airways Airbus A-310 crashed into the sea shortly after takeoff from Abidjan, killing 169 of the 179 passengers and crew.

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