Kinshasa - Heavy gun and mortar fire shook the Congolese capital Kinshasa at first light on Friday in a second day of fighting between government troops and forces of a former rebel leader who lost last year's presidential polls.

Congo's state prosecutor has issued an arrest warrant for high treason against former rebel leader Jean-Pierre Bemba, a presidency official said.

The battles, the first in the city since landmark election last year won by President Joseph Kabila, started on Thursday when Bemba's forces defied a government order to disarm.

"This is a rebellion ... He has committed high treason," Antoine Ghonda, roving ambassador attached to Kabila's presidency, told Reuters. He said the state prosecutor had issued a warrant for Bemba's arrest.

South Africa's foreign ministry said late on Thursday that Bemba had taken temporary refuge in its embassy in the city.

One column of smoke rose from the area of an oil refinery early on Friday, a resident said, and a Reuters witness saw another plume of smoke coming from the vicinity of Bemba's residence in the city's plush Gombe district, which has seen the worst of the fighting.

Several people including civilians have been killed in the fighting, a hospital doctor and other witnesses said.