MADRID/BRUSSELS (Reuters) - Spain shut 19 northern airports including Barcelona on Saturday because of the cloud of abrasive ash blowing south from a volcano in Iceland.

The government said over 400 flights would be canceled, leaving almost 40,000 people stuck in airports stretching from La Coruna in the northwest to Barcelona in the northeast.

Air traffic was expected to be affected until 2 a.m. Sunday (10 p.m. EDT Saturday), at which time flights would gradually resume.

However, Spain’s airport authority said that from 1800 GMT three airports - Zaragoza, Valladolid and Salamanca - would re-open. It said Barcelona’s should re-open at 2 a.m. on Sunday given current forecasts for the ash’s trajectory.

The government said there was a chance the cloud could still affect Spain next week.

“We don’t rule it out and we will make alternative plans,” Transport Minister Jose Blanco told a news conference.

Extra places had been made available on long-distance trains and extra buses and boats were being laid on to help people reach their destinations, he said.

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Transatlantic flights were being re-routed around the affected area, causing substantial delays.

Sweeping closures of European airspace last month disrupted the travel of millions of passengers in Europe and elsewhere, and cost airlines over a billion euros in revenues.

Scientific assessments led to a decision to restrict closures to areas of higher ash concentration, after lower concentrations were found not to be damaging aircraft engines.

The European air traffic agency Eurocontrol warned on Saturday of a rise in emissions from the volcano, Eyjafjallajokull.

“The area of potential ash contamination is expanding in particular between the ground and 20,000 feet,” it said.

But fears that the ash would shut airspace over Portugal and southern France were not immediately borne out.

Authorities said problems could begin in France by Monday.

“Logically, we will be spared until Monday noon, based on current forecasts,” a French aviation authority spokesman said.

Air France said late on Saturday it had carried out a test flight over the Bay of Biscay and Pyrenees without finding any traces of ash. It had no plans to cancel flights.