MONTREAL - Ongoing student unrest has prompted warnings of economic disruption in Montreal and even a security message issued by the U.S. government.

American tourists were warned of possible "unforeseen violence," "vandalism" and "arrests," in a message issued Apr. 27 by the U.S. embassy in Ottawa to visitors heading to Montreal.

The message warned Americans traveling to Montreal that although businesses remain open, traffic and public transportation may be disrupted. Tourists are told they could run into demonstrations and, while most of them have been peaceful, some can turn "potentially violent."

U.S. diplomats went out of their way Friday to downplay the significance of the memo; they called various media outlets to point out that it was to be referred to as a "security message" and should in no way be confused with travel warnings like those issued to 31 countries including Syria, Haiti and Iran.

They billed it as a routine diplomatic message.

"When we issued this security message, there was an enhanced police presence and some of the demonstrations had been violent. Rocks were thrown and there were instances of vandalism," a consular official said.

He said the embassy in Ottawa is required to provide information under a "no-double-standard policy," meaning consulates have to make sure that whenever they have information about certain threats they must share it with American citizens.

News of the American message, which had largely gone unnoticed, spread in the local media Friday and fuelled speculation about whether three months of disquietude might ultimately harm the local economy.

Such fears are intensifying now that the summer festival season is approaching. Montreal's famous comedy and jazz festivals, and Formula One parties, tend to be concentrated near the streets and public squares that have been awash in frequent protests.

One student association, comprising arts majors at UQAM university, decried this week that the protest movement had actually been too peaceful.

The association has a new objective, laid out in a motion adopted this week: to force the cancellation of the Formula One Grand Prix, an event its motion decried as a vessel for sexist, anti-environmental, elitist jet-setters.

Calculating the potential economic impact of ongoing unrest is no easy task.

According to the Board of Trade of Metropolitan Montreal, just the 90-minute delay caused Thursday by smoke bombs in several metro stations cost $11 million in lost productivity. The Montreal Economic Institute, a conservative think-tank, came up with its own figure of $9.3 million.

The disruptions have been so frequent, and so varied in size, that it's hard for economists to accurately pinpoint the economic fallout. Daily events have ranged from brief and peaceful street demonstrations, to riotous scenes, to this week's shutdown of metro service during rush hour.

The president of the Board of Trade of Metropolitan Montreal, Michel Leblanc, said there are too many variables to consider.

"Some businesses only closed down for short periods of time when the protests were violent," he said. "Then you have to factor in delays -- people were late getting to work because of the metro and bridge disruptions -- that affect logistics and the productivity of businesses."

He says Montrealers are now developing habits to avoid the downtown core because of fears originating from the recent protests.

Leblanc said people don't fear violence as much as they fear delays caused by the protests -- like being late for work or getting stuck in a traffic jam.

"The fear now is that downtown Montreal may fragilize as a result of these protests. And we know very well that the strength of a strong metropolis lies in its ability to have a strong downtown area."

Local merchants are visibly fed up.

Steve Siozos, president of the Crescent Street Merchants Association, said businesses in his association have suffered a 20 per cent decrease in revenue this year and he says it's getting progressively worse.

He says he's already seen indications of an impact on the Grand Prix weekend of June 8-10. He has heard that there have been fewer hotel reservations, compared to last year.

Mayor Gerald Tremblay expressed frustration when asked about the economic disruption the city has been experiencing.

"What do you want me to do? Are we going to stop living because we have a crisis on our hands? No. What's the solution? That's the question," Tremblay told reporters at a news conference after Thursday's most recent metro disruption.

Coverage of the protests, complete with descriptions of confrontations between students and riot police, certainly is a topic of conversation among some potential tourists to Montreal.

One Internet user from Massachusetts shared his fears on the Trip Advisor forum.

"I hate to say it as we go up several times a year, and stay downtown, but I might think twice if I was going up now," he said.

"It is not that I'm worried about getting into the middle of anything, but rather the irritation and having to avoid or leave an area you might otherwise enjoy."