Malawians headed to polling stations on Tuesday for presidential and legislative elections seen as a tough test for President Peter Mutharika, who is facing challenges from the deputy president and a former pastor who heads the opposition.

Malawi is heavily dependent on foreign aid and is frequently beset by droughts which threaten the lives of thousands of people.

Former law professor Mutharika, 78, oversaw infrastructure improvements and a sharp reduction in inflation in his first five-year term, but critics accuse him of corruption and cronyism.

Mutharika refutes those accusations.

Reuters reporters saw voters casting ballots in Blantyre and Lilongwe, two of the largest cities in the southern African country.

"I have a strong feeling that the choice I made will carry the day," said Tima Nyirongo, a 31-year-old mother of two who voted at Chirimba School in Blantyre.

Polling stations opened at around 0400 GMT. Some 6.8-million registered voters will cast ballots for president, parliament and ward councillors.

Analysts expect a tight presidential race between Mutharika, Deputy President Saulos Chilima and Lazarus Chakwera, who heads opposition group the Malawi Congress Party.

Chilima, a 46-year-old former telecoms executive, quit Mutharika's Democratic Progressive Party last year and formed his own party to run against Mutharika.

He has targeted the youth vote with a vibrant social media campaign featuring hip-hop videos.

Chilima and Chakwera, 64, have both promised to crack down on corruption.

Chakwera lost out to Mutharika in 2014 elections and has formed an alliance with Mutharika's predecessor, Joyce Banda, this time.