Swiss airspace “has been re-opened since 8:00 am local time”, a spokeswoman for the Federal Office of Civil Aviation said, refusing to say whether the lifting of the flight ban would remain in place.

At Zurich airport, operations were “starting up slowly” with many flights still cancelled, a spokeswoman said. A first flight left at 8:30 am for the Egyptian Red Sea resort of Sharm el-Sheikh

Geneva airport also saw operations pick up slowly, according to a spokesman who said that “it would take several hours or even several days to return to normal.”

He urged passengers to check their flights with their airlines before coming to the airport.

Swiss aviation authorities decided on Monday that the volcanic ash cloud had decreased enough to reopen the country’s airspace on Tuesday morning after test flights by military aircraft and the Swiss airline.