LUSAKA, Zambia -- Zambia's president led Monday in nearly complete results from an election whose vote-counting process has taken days and prompted opposition allegations of irregularities.

With 132 of Zambia's 156 constituencies counted, President Edgar Lungu of the ruling Patriotic Front party had 1,454,165 votes while Hakainde Hichilema of the opposition United Party for National Development had 1,383,594 votes, according to election officials.

Most of the remaining 24 constituencies are ruling party strongholds, the Zambia Daily Mail reported.

Zambia's election Thursday followed a tense campaign marred by street clashes, though the voting day was mostly peaceful. Lungu, who took office in January 2015 after the death of President Michael Sata, won a tight race over Hichilema in an election last year. The rules have since been changed to require a candidate to win more than 50 per cent of the vote or face a runoff election.

Zambia's record of peaceful transitions of power had been held up as a democratic model in Africa. International observers have appealed for calm and urged Zambians to direct any complaints about the election process to the courts, rather than taking to the streets.

"In this tense and competitive climate it is essential that the security forces respect the constitution and remain impartial and professional in the discharge of their duties," said Kofi Annan, the former U.N. secretary-general.

The Carter Center, the human rights organization founded by former U.S. President Jimmy Carter, said the weeks ahead will test Zambia's democratic institutions.

"The country still faces significant challenges as its nascent dispute-resolution processes will surely be tested for the first time," the centre said in a statement.