Eurocontrol, which is the European organisation responsible for the safety of air navigation, on Thursday said Ukrainian authorities had closed air routes in eastern Ukraine following the crash of Malaysian Airlines flight MH17.
All flight plans filed using these routes were now being rejected, Eurocontrol said, and added that the routes will remain closed until further notice. A crisis cell was being activated to co-ordinate the response to the impact of the airspace closure.
The International Air Transport Association (IATA) said: “Based on the information currently available it is believed that the airspace that the aircraft was traversing was not subject to restrictions”.
Tytgat Luc, director of Eurocontrol, told BBC Radio 5 Live that there were four aircraft flying in the same area at the same time that the crash occurred, but that they continued their flights. Eorocontrol had warned airlines in April to avoid the area above the conflict zone in Ukraine.
Britain’s Department of Transport said in a statement: "Flights already airborne are being routed around the area by air traffic control in the region. Pilots around the world have been advised to plan routes that avoid the area by Eurocontrol”.
Air France, Virgin Atlantic, and the German airlines Lufthansa announced rerouting flights to avoid the area.
Lufthansa said it had decided to "fly a wide detour around east Ukrainian airspace with immediate effect", and added that the decision would affect four of its flights on Thursday. "The safety of our passengers is our top priority," a spokesperson added.
A spokesperson for Virgin Atlantic said it would re-route "a small number" of its flights following the incident, but added that "we do not anticipate significant delays and are planning for increased flight lengths on impacted flights of approximately 15 minutes."
Meanwhile, Peter Felsted, editor of Jane's Defence Weekly, said sophisticated weaponry would have been needed to take down a flight travelling at an altitude of 10,000m (33,000ft).
He told the BBC: "Those kind of systems are obviously in the Ukrainian inventory as much as the Russian inventory, but I would say it's much less likely that the Ukrainian rebels who would have had control of one of these systems."
There were unconfirmed reports that there were some British citizens on the flight.
A statement from 10 Downing Street said: “British officials were due to meet this evening to take stock of the Malaysian air disaster, including the possibility that British nationals were on board. It is likely that meeting will be largely practical and an assessment of what is known, as opposed to any ministerial political action”.