LUSAKA: Two demonstrators were killed on Wednesday in a protest outside the police headquarters in the Zambian capital Lusaka, where opposition leader Hakainde Hichilema was being interviewed, an AFP reporter said.

Police arrived to break up a crowd of several hundred demonstrators and shots were heard, leaving the blood-stained bodies of two men on the ground after the crowd fled, he said.

Police issued a statement saying that two people were reportedly killed by gunfire after tear gas was used to disperse an unruly crowd, and that the circumstances were not immediately clear.

Hichilema, 58, is the main contender to President Edgar Lungu in elections due next August.

A veteran campaigner and self-made entrepreneur, he bid five times for the presidency between 2006 and 2016.

After narrowly losing in 2016, he spent four months in jail when he contested the outcome.

Hichilema has vowed to step down as leader of the United Party for National Development (UPND) if he fails again next year.

Lungu, 63, is struggling with a wave of unpopularity and internal divisions within his party, fuelled especially by Zambia's economic problems.

The country is heavily dependent on copper, demand for which has slumped.

The reason why Hichilema was called to police headquarters was not immediately known.