A man has been shot dead in southern Chad during Monday's presidential election.

Electoral officials said the unknown assailant was among a group of people who'd stormed into a voting station in the city of Moundou demanding their right to vote be upheld.

The victim was a 65-year-old man. The local mayor said four people were arrested.

Earlier, one presidential candidate, Mansiri Lopsikreo, had claimed there were irregularities in some polling stations.

He also said unnamed influential representatives of a political party allowed hundreds of their supporters to vote without electoral cards, "sometimes two or three times in certain stations".