Opponents of a bid by Burundi's president to seek a contested third term in office on Sunday called for even bigger street protests after a day of violent clashes with police.

"We are calling on residents of Bujumbura to protest against the third mandate for Pierre Nkurunziza in even greater numbers tomorrow," said Vital Nshimirimana, head of a prominent NGO forum and the main leader of the campaign to block a third term.