Police arrested some 400 people in Montreal early on Thursday after demonstrators threw rocks at officers in the latest student protest to shake the city, a police spokesman said.

Several thousand demonstrators poured into Montreal's central square late Wednesday in an unsanctioned rally, defying a law passed last week requiring organizers to notify authorities eight hours ahead of public demonstrations.

Police moved in after several hours when some of the demonstrators threw rocks at them, police spokesman Daniel Lacoursiere said.

Protests have raged in Montreal since mid-February over a plan by provincial Premier Jean Charest to raise tuition fees at Quebec universities by 82 percent to rein in a budget deficit.

Some of the demonstrations have turned violent, with store fronts smashed.