Canadian Grand Prix organisers have cancelled a free access day for spectators at the Montreal Formula One circuit due to fears that student protesters may try and disrupt the event.

A statement on the official grand prix website said there would be no Thursday 'Open Doors' day, an important and popular part of the build-up to Sunday's race.

"Following a serious examination of the situation, made necessary by public disruption threats and the difficulty to measure their precise validity, the organisers came to the conclusion that it is necessary to restrain the access to Circuit Gilles-Villeneuve and precisely the F1 pit lane," it said.

Francois Dumontier, president of the race, said the risks could not be ignored.

"One of our primary obligations is to ensure the comfort and the security of the participants and the spectators, something we will do as we open the turnstiles Friday morning, and again during the whole weekend," he said.

"Considering the various disruption threats made public recently, the free admission and the naturally open character of the 'Open Doors' day revealed some risks that we could not neglect.

"Under these circumstances, cancelling the 'Open Doors' day was the only action we could take."

The sometimes violent student strike began in mid-February after the Quebec provincial government announced plans to raise tuition fees.

Tourism is a major source of revenues for Montreal and the race attracted some 300,000 people last year according to the local tourism authority.