Volcanic ash from Iceland snarled air traffic across Europe for a second straight day Friday, causing the cancellation of some 17,000 flights, according to the intergovernmental body that manages European air travel.

Eurocontrol said it expected around 11,000 flights to take place Friday, in contrast to the normal 28,000. The impact will last at least another 24 hours, Eurocontrol said Friday morning.

The ash has forced the closure of some of Europe’s busiest airports in what is the most significant disruption to worldwide air travel since 9/11.

Airspace over much of the United Kingdom was closed to all flights except emergencies at least until 1 a.m. Saturday (8 p.m. ET Friday), Britain’s air traffic authority, NATS, said. Select flights were being allowed in Northern Ireland and Scotland, and some North Atlantic traffic may be allowed to those areas, it said.

Airspace was also closed over Belgium, Denmark, Finland, Lithuania, Estonia, and the Netherlands, and airspace was partially closed in France, Germany, Poland, Sweden, Norway, and Ireland, Eurocontrol and local authorities said.

(Read More: CNN)