A burst of gunfire has rung out in the Philippine Senate, where authorities have tried to arrest a senator who is wanted by the International Criminal Court for a charge of crime against humanity.

It was not immediately clear what set off the gunfire on Wednesday night or if there were injuries in the Senate, where senator Ronald dela Rosa has stayed in protective custody by allied senators as Philippine authorities tried to arrest him and possibly turn him over later to the ICC.

On Monday, the ICC unsealed an arrest warrant for dela Rosa, a former national police chief who first enforced then-president Rodrigo Duterte's anti-drug crackdowns, in which thousands of mostly petty suspects were killed.

Originally issued in November, the warrant charges dela Rosa with the crime against humanity of murder of "no less than 32 persons" between July 2016 and the end of April 2018, when he led the national police force under Duterte.