Toronto travellers are feeling the effects of an ash-spewing volcano in Iceland that grounded planes across much of northern Europe on Thursday, causing travel disruptions not seen since the terror attacks of Sept. 11, 2001.

British airspace shut down on Thursday, silencing the transatlantic hub of Heathrow in London and leaving tens of thousands of passengers scrambling to make other arrangements.

At Pearson, Canada's busiest airport, many Europe-bound travellers were awaiting word about the status of their flights on Thursday. The Toronto Airports Authority reported 11 Europe-bound flights had been cancelled as of 5 p.m. ET.

"We were supposed to fly out at 6 p.m. tonight. Now we're starting to wonder if that's going to happen," traveller Barbara Shutt told CBC News. Shutt was planning to fly to London to reach her home in Hereford, England, near the Welsh border.

"It's not looking good," she said. "The best prognosis is that [the departure] will be seven in the morning. It's going to be a long day and a long night. But I'd rather have my feet on the ground if there's going to be a problem."

'A bit worrying'

Carolin Hackwell was also at Pearson awaiting word about her flight home to the U.K. Toronto was the last leg of a journey that had taken her to Australia, Hawaii and Fiji.

"It's a bit worrying, but there's not a lot you can do about it," said Hackwell.

Air Canada said it has cancelled all flights to and from Heathrow, as well as Charles de Gaulle airport in Paris and the Frankfurt airport until further notice. Air Transat nixed all flights to Heathrow.

Aircraft grounded by civil aviation authorities sit idle at Belfast City airport on Thursday. (Peter Morrision/Associated Press)

Shutdowns and cancellations spread through the U.K., France, Belgium, the Netherlands, Denmark, Ireland, Sweden, Finland and Switzerland.

University of Toronto geology professor James Brenan told CBC News that because volcanic ash is abrasive, it poses a serious danger to jet aircraft.

"If this stuff gets inside the engine, it's basically glass and causes the engine to shut down," said Brenan.

The U.S. Geological Survey said about 100 aircraft ran into volcanic ash from 1983 to 2000. In some cases, engines shut down briefly after sucking in volcanic debris, but there have been no fatal incidents.

In 1989, a KLM Royal Dutch Airlines Boeing 747 flew into an ash cloud from Alaska's Redoubt volcano and lost all power, dropping from 7,620 metres to 3,660 metres before the crew could get the engines restarted. The plane landed safely.

In another incident in the 1980s, a British Airways 747 flew into a dust cloud and the grit sandblasted the windshield. The pilot had to stand and look out a side window to land safely.

Aviation officials in Europe said it was not clear when it would be safe to fly again and said it was the first time in living memory that an ash cloud had brought one of the world's most congested airspaces to a standstill.

A scientist in Iceland said the erupting volcano could eject tonnes of ash into the air for days or even weeks, while meteorologists from the AccuWeather forecasting service in Pennsylvania said the current ash plume will threaten Europe at least through Sunday.

"Depending what happens and what the cloud does, this could last a couple of days," said Kyla Evans, a spokeswoman for air traffic agency Eurocontrol in Brussels.

With files from CBC's Muhammad Lila and The Associated Press