Thousands of flights and untold numbers of travelers were affected as some of Europe's busiest airports closed, including London's Heathrow, Amsterdam's Schiphol, and Paris' Charles de Gaulle. Volcanic ash can cause jet engines to shut down.

The prime minister of Norway was among those stranded by the closure of European airspace.

Airspace over much of the United Kingdom was closed to all flights except emergencies at least until 7pm on Friday.

France, Germany, Ireland, Sweden, Norway, Belgium, Denmark and the Netherlands also announced the complete or partial closure of their airspace, said authorities in each country.

It is hard to predict how long it will be before air travel can resume, said Matthew Watson, a geophysicist at England's Bristol University.

In all, around 3,000 flights across Europe were expected to be affected by the closures, according to Eurocontrol, the intergovernmental body that manages European air travel.