Malawian President Peter Mutharika leads his main rival in this week's election winning more than 40 percent of votes cast, according to figures released on Thursday with three-quarters of votes counted.
President Mutharika, who heads the ruling Democratic Progressive Party (DPP) and is fighting for a second five-year term, has 40.49 percent of the vote, the Electoral Commission said.
Opposition leader Lazarus Chakwera had 35.44 percent, while Vice President Saulos Chilima was on 18 percent, according to the partial results.
Mr Mutharika, 78, campaigned for a second five-year term on his record of improving Malawi's scant road and power infrastructure.
But his government has been dogged by several high-profile cases of corruption and nepotism.
Mr Chakwera on Wednesday warned of alleged attempts to rig Tuesday's election, saying his Malawi Congress Party (MCP) was conducting its own count that showed he was ahead.
The southeastern African country has around 6.8 million potential voters, with more than half aged under 35.
Turnout data has not been published.
Voters also chose lawmakers and local councillors in Tuesday's elections.
The European Union observer mission described the vote as "well-managed, inclusive, transparent and competitive".
But it said that tension during the campaign "was not helped by various claims of 'rigging'".
There was "an unlevel playing field", observers said, without giving further details.
Malawi has a "winner-takes-all" system and in 2014 Mr Mutharika won with just 36 percent of the vote.
He came to power vowing to tackle corruption after the "Cashgate" scandal erupted a year earlier, revealing massive looting from state coffers.
But he has also faced corruption allegations.
Last November, President Mutharika was forced to return a $200,000 (180,000 euro) donation from a businessman facing a corruption case in a $3-million contract to supply food to the Malawi police.
At his final campaign rally last weekend, Mr Mutharika told supporters in Blantyre: "My priorities for this country are development and building skills."
Former evangelist Chakwera, 64, came second to Mr Mutharika in the 2014 polls.
Mr Chilima was a member of the ruling party but quit last year to form the youth-focused United Transformation Movement, while staying on as vice president.
Under Malawi law, the President cannot fire the vice-president.
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.
The country, which has a population of 18 million people, has one million adults living with HIV -- one of the highest HIV prevalence rates in the world.