At least 13 people were killed and dozens injured as government forces opened fire on peaceful protesters in two cities in Nicaragua as anti-government demonstrations threatening to bring down the president continued.

Hundreds of thousands of Nicaraguans had marched through the capital of Managua on Wednesday, many dressed in black to mourn the more than 80 people killed since protests began.

As marchers gathered around the end-point at the University of Central America (UCA), shots rang out a few hundred metres away. Families with children desperately fled the scene. The rector of UCA said thousands of people took refuge on its campus.

Footage shows that shots came from both snipers in plain clothes firing from surrounding buildings, and riot police on foot.

Katherine Martinez, 22 a stay-at-home mum, was with her husband outside the nearby University of Engineering when the shooting began.