From the BBC:
Police in Hong Kong have used water cannon and tear gas against protesters throwing petrol bombs and bricks near government offices in the city.
The violence broke out after thousands of pro-democracy demonstrators marched, despite being denied a police permit.

Scuffles also broke out later between rival protesters around the city.

Earlier hundreds rallied outside the British Consulate, demanding the UK press China to maintain freedoms guaranteed during the 1997 handover.

The months of unrest were sparked by a proposed extradition bill, which would have made it possible for people in Hong Kong to be extradited to mainland China. Critics said they could have faced human rights abuses.