He was forced from Honduras at gunpoint in June, and replaced by Roberto Micheletti. They are not candidates.

The favourite to win is conservative Porfirio Lobo from the National Party, and Elvin Santos from the Liberal Party is considered his nearest rival.

Mr Zelaya's supporters have called on voters to boycott the election.

Mr Lobo, 61, narrowly lost to Mr Zelaya in 2005, and Mr Santos, 46, was previously Mr Zelaya's vice president in the divided Liberal Party.

Polling stations are due to open at 07.00 (13.00 GMT) and close at 16.00 (22.00 GMT).

About 30,000 soldiers and police are to provide security for the elections, but many fear violence could erupt.