Twenty Spanish airports in the northern part of the Iberian peninsula were closed Saturday due to the cloud of ash from the Icelandic volcano of Eyjafjalla, which covered part of Spanish air space.

The decision, which follows the recommendation of the European Organization for the Safety of Air Navigation, or Eurocontrol, was taken by Spain’s Public Works and Transport Minister Jose Blanco, with the “absolute priority” of guaranteeing passenger safety.

The minister announced these measures at a press conference after a meeting of the State Commission for Airport Monitoring.

This agency was created Friday to track the effects of the volcanic cloud, which in recent weeks has skirted Spain’s northern coast until winds blew it onto the peninsula.

The cloud, which limits visibility and puts air navigation at risk, brought about the closure Friday night of the northwestern airport of Santiago de Compostela, and Saturday morning kept from opening those in Vigo, La CoruAsturias, Santander, Leon, Burgos, Valladolid and Salamanca, all in the northern half of Spain.

The number of airports closed down increased to 16 by noon Saturday, with the additional shut—downs of facilities in Bilbao, Vitoria, San Sebastian, Pamplona, Zaragoza, La Rioja and Lerida.

Taking note of how the winds were evolving and, after government insistence that it will authorise no flights as long as technicians cannot “fully” guarantee that the cloud of volcanic ash has cleared away and “holds no risk for aircraft”, it was obligatory to shut down four more airports, putting the total at 20.

The last airports to close down temporarily Saturday were four in Catalonia, including Barcelona—El Prat — one of Europe’s biggest — Sabadell, Girona and Reus, following Blanco’s estimate that the cloud of ash will extend all the way to the peninsula’s northeast.

“It is our responsibility, and I believe that everyone will understand, to act according to the criteria of complete safety for passengers”, who could number 28,000 affected in the case of Barcelona airport alone, where 320 of the 648 scheduled flights will be suspended.

In order to ease the problems caused by airport closures, Spain’s RENFE railways, some airlines along with transport companies by sea and by road have offered passengers alternative ways to get where they are going.

The capacity of trains and ships has been increased, as has that of highway transportation, to guarantee “mobility at all times for the people who need it”, Mr. Blanco said.

In the coming hours — but only if the expected conditions prevail — service could be re—established in most airports by 8 p.m., when all Spain will be able to open most of its air space.

But until more information is available on how the cloud is evolving, the transport minister cannot dismiss the possibility that “throughout the week” there could be problems if the cloud returns over Spain.