Zambian police arrested 151 opposition supporters after riots erupted over President Edgar Lungu's controversial election victory, police said Tuesday.

The arrests came after protesters set five buildings on fire, stoned houses and blocked roads in Southern Province, police spokesman Rae Hamoonga said in a statement.

The suspects would soon appear in court, he said, adding that the situation was ‘under control.’  Southern Province police commissioner Goodwin Phiri said four senior police officers had been beaten by protesters in the town of Mazabuka.

The riots followed the announcement by the electoral commission on Monday that Lungu had taken a narrow victory in the August 11 elections.

Opposition leader Hakainde Hichilema accused Lungu of fraud. His United Party for National Development (UPND) was expected to challenge the result in court.

Zambia is regarded as one of Africa's most successful democracies, with many peaceful changes of power having taken place since multi-party democracy was introduced in 1990.

But these elections were preceded by a wave of violence, with clashes erupting between opposition and government supporters. Police also broke up opposition campaigning and shot two UPND supporters dead.

Lungu, 59, became president after narrowly winning a January 2015 presidential by-election caused by the death of his predecessor, Michael Sata.

The opposition accuses the PF of not having been able to contain an economic downturn sparked by falling prices of copper, the country's main revenue earner. It also blames the government for not tackling drought-induced electricity shortages, which triggered a steep fall of the kwacha currency and spiralling inflation.