Malawi's top court on Thursday began hearing an opposition application to overturn the results of the presidential elections held three months ago, over alleged election irregularities.
The hearing comes after the Malawi Congress Party (MCP), the largest opposition, and the United Transformation Movement (UTM) lodged complaints of alleged fraud in the May 21 election.
President Peter Mutharika, leader of the ruling Democratic Progressive Party (DPP), held onto power in the vote, narrowly defeating Lazarus Chakwera of the MCP.
Chakwera alleges he was the rightful winner of the election, which he lost by 159,000 votes and described the results as "daylight robbery."
Opposition leaders have claimed that results sheets were altered using correction fluid.
UTM leader and former vice president Saulos Chilima was the first to take the witness stand after the defence failed in its attempts to force a postponement of the hearing on Thursday.
Security forces were deployed around the court premises, where a small crowd of opposition supporters also congregated.
When the court met last month for preliminary hearings, police used tear gas to disperse opposition supporters gathered outside.
Mutharika has dismissed doubts over him winning 38.57 percent of the vote, saying international observers had deemed the May 21 election "peaceful, free and fair."
Malawi won independence from colonial ruler Britain in 1964, and was then ruled by Hastings Banda as a one-party state until the first multi-party elections in 1994.