Europe's busiest airport closed early Monday morning as a dense clowd of volcanic ash drifts across England from Iceland, aviation authorities said.
The airspace over London's Heathrow Airport closed at 1 a.m. Monday, Britain's National Air Traffic Service said in a statement late Sunday night.
The restrictions affecting Heathrow — as well as Gatwick, Stansted, and London City airports — will be in place until at least 7 a.m. Monday, the aviation authority said.
Airports across Britain and Ireland were closed for much of Sunday because of the drifting ash. The shifting of the no-fly zone southward will allow airports in northern England — including the key cities of Manchester and Liverpool — to reopen after 1 a.m.
But all airports in Northern Ireland, as well as some Scottish facilities, will remain shut.
In Ireland, Dublin's international airport closed early Sunday evening until at least 12 p.m. Monday (1100 GMT, 7 a.m. EDT). Some airports in Ireland's west were closed and will reopen at different times Monday, but Shannon and southern Cork were open "until further notice."
The British air traffic agency said the ash cloud was changing shape and moving south, toward Oxford, England, 60 miles (100 kilometers) northwest of London. Britain's weather service says the northwest winds should shift midweek, redirecting the ash away from Britain.
German authorities sent up two test flights Sunday to measure the ash cloud, one from the German Aerospace Center and the other from Lufthansa, the country's biggest airline.
The DLR plane flew to southern England then continued north, collecting data from between 10,000 to 23,000 feet (3,000 to 7,000 meters). The Lufthansa Airbus A340-600, equipped with special scientific gear, left Frankfurt to fly over northern Germany, the United Kingdom and parts of Scandinavia.
All the data from both flights was immediately sent to aviation authorities in the U.K, the Netherlands and Germany, said aerospace center spokesman Andreas Schuetz.