Zambian President Hakainde Hichilema's lead in the Southern African country's presidential election has widened, partial results from about 71% of constituencies showed on Monday.

Hichilema's share of the valid votes rose to roughly 62%, up from 59% late on Sunday.

His main challenger, Brian Mundubile, was on 36% of valid votes, down from 39% overnight.

A presidential candidate must receive more than 50% of the vote to win in the first round, or face a run-off between the top two contenders.

Analysts had predicted Hichilema, 64, would win the election due to the advantages of incumbency and a fractured opposition, although Mundubile drew large crowds during campaigning.

Zambia is the continent's second-largest copper producer after Democratic Republic of Congo and is of strategic interest for its critical minerals.

Late on Sunday Zambia's government said police had arrested several leading opposition figures on the night of the election on August 13, accusing them of posing a threat to state security.

Opposition parties and civil society groups accused the government of growing repression in the lead-up to the election, including placing restrictions on their meetings and campaign activities. The government has denied the accusations.