Britain reopened its airspace Tuesday in line with most other European countries, clearing the way for thousands of stranded passengers to resume travel following massive disruptions caused by a plume of ash from a volcano in Iceland.

Flights resumed just before 10 p.m. local time (5 p.m. ET). The first jet to land in London since last Thursday was a British Airways plane from Vancouver.

The reopening means thousands of flights can resume to and from Heathrow and Gatwick airports. A base for more than 90 airlines flying to more than 90 countries around the world, Heathrow calls itself "the hub of the aviation world."

The reopening will occur in phases, Britain's Civil Aviation Authority announced late Tuesday.

"There will continue to be some 'no fly zones,' where concentrations of ash are at levels unsafe for flights to take place, but very much smaller than the present restrictions," the agency said on its website.

Air Canada, which had earlier cancelled all Tuesday flights to Heathrow from Toronto, expected to resume flights at least partially on Wednesday morning.

The gritty volcanic ash, which limits visibility and can damage an airplane's engines, is spewing from a volcano in Iceland's Eyjafjallajokull glacier that erupted last Wednesday for the second time in less than a month.

The British National Air Traffic Service said earlier Tuesday that airspace above Scotland and parts of northern England had been partially reopened, but lingering ash was forcing it to keep major London-area airports closed.

In northern Europe, some planes were able to move through Milan, Amsterdam and Paris on Tuesday, but several flights through the area were still cancelled. The Netherlands officially opened its airspace to all flights by late in the day, and France planned to allow long-haul departures and arrivals starting Wednesday.

The first commercial flight out of Paris's Charles de Gaulle airport since last Thursday headed to New York's JFK airport. Others are scheduled for San Francisco, Algiers and other faraway destinations.

"We were in the hotel having breakfast and we heard an aircraft take off. Everybody got up and applauded," said Bob Basso of San Diego, who has been staying in a hotel near Charles de Gaulle airport since his flight Friday was cancelled.

Eurocontrol, the air traffic control agency, said it expected slightly less than half of Europe's 27,500 flights to go ahead Tuesday, a marked improvement over the last few days. More than 95,000 flights were cancelled in the last week alone.

While most air corridors across Europe have been given the green light, airlines are scrambling to get planes and crews in place, leading to flight bottlenecks. Eurocontrol predicts that takeoffs will be close to normal by Friday, but airlines face the enormous task of working through a massive backlog to get passengers where they want to go — a challenge that could take days or even weeks.

Passengers with current tickets were being given priority — stranded passengers were being told to pay for a new ticket, take the first available flight or use their old ticket and wait for days, or weeks, for the first available seat.

The disruption, which British Prime Minister Gordon Brown called "the biggest challenge to our aviation transport network for many years," has cost European airlines roughly $1 billion US in lost revenue.

Volcano still active

The volcano in southern Iceland is still spewing smoke and lava, but the ash plume is lower than before, posing less threat to high-flying aircraft.

Still, scientists worry the activity could trigger an even larger eruption at the nearby Katla volcano, which sits on the massive Myrdalsjokull icecap and has erupted every 80 years or so — the last time in 1918.

"The activity of one volcano sometimes triggers the next one, and Katla has been active together with Eyjafjallajokull in the past," said Pall Einarsson, professor of geophysics at the Institute of Earth Sciences at the University of Iceland.

"I think it is high time for European governments to start planning for the eventual Katla eruption," Icelandic President Olafur Grimsson warned Tuesday.

Still stranded

Stranded travellers have been camped out in hotels and airports for days as they wait for flights.

Janay Nugent-Moulton is one of 200 Canadians stuck in London who have checked in at the Canadian High Commission. She was scheduled to leave on April 17, but the airline told her the earliest flight available is on April 25.

"This is costing a lot of people a lot of money," she said. "There's family obligations, work obligations, it's really a hardship for a lot of people."

Nugent-Moulton said she would like the High Commission to help stranded Canadians book alternative travel arrangements and find affordable accommodations.

Meanwhile, the first of three British warships being sent to carry travellers home from Europe has arrived in Spain. HMS Albion docked in Santander, a port in northern Spain, on Tuesday morning, and will carry a group of British soldiers and travellers back to the U.K.

A cruise ship was due to leave later in the day to pick up about 2,000 British tourists in the northern Spanish port of Bilbao.

With files from The Canadian Press, The Associated Press