Hakainde Hichilema, leader of the United Party for National Development and Zambia's opposition leader, has been declared winner of the recently held presidential election, defeating incumbent Edgar Lungu.

Hichilema will become Zambia's seventh president after amassing over 2.8 million votes against Lungu's 1.8 in the Aug 12 general election. Esau Chulu, chair of the Electoral Commission of Zambia, announced the results early Monday, saying the returns came from 155 constituencies out of 156.

"I therefore declare the said Hakainde Hichilema to be president-elect of the Republic of Zambia. The outstanding results are not likely to materially influence the overall results of this election. Therefore, the consolidated results are for 155 constituencies out of 156," Chulu said.

Having taken an early lead and widening the gap as results came in, Hichilema took to social media to call for calm and peace as the country prepared for change.

"With victory in sight, I would like to ask for calm from our members and supporters. We voted for change and for a better Zambia that is free from violence and discrimination. Let us be the change we voted for and embrace the spirit of Ubuntu to love and live together harmoniously," Hichilema said in a Twitter message on Sunday.

Lungu released a statement on Saturday claiming the election was neither free nor fair due to incidents of violence reported in what is traditionally Hichilema's stronghold.

The election, whose turnout was estimated at more than 70 percent, marked the sixth time Hichilema has run for Zambia's presidency. In the last elections in 2016, he narrowly lost to Lungu by about 100,000 votes.

International election observers have commended the transparent and peaceful organization of the polls while condemning restrictions on freedom of assembly and movement during the election campaign.

In its preliminary statement, the African Union Election Observation Mission to Zambia asked all parties to refrain from acts of violence, hate speech, incitement,and intimidation of opponents during the electoral process.

"Aggrieved parties should channel any disputes on the process or its outcomes through appropriate dispute resolution mechanisms as provided for in the law," the mission said in a statement.

According to Zambia's constitution, any contender who wants to settle a dispute or nullify elections must approach the country's Constitutional Court within seven days of a winner being announced to lodge a complaint.