Ukrainian authorities on Thursday declared the east of the country a no-fly zone after a Malaysian airliner carrying 295 people crashed in the volatile region, European flight safety body Eurocontrol said.
European and US airlines rerouted their flights as Kiev said the Malaysia Airlines flight MH17 was shot down in a "terrorist" attack and a US official said intelligence analysts "strongly believe" it was downed by a surface-to-air missile.
"Since the crash, the Ukrainian authorities have informed Eurocontrol of the closure of routes from the ground to unlimited (altitude) in Eastern Ukraine," a statement said.
"All flight plans that are filed using these routes are now being rejected by Eurocontrol. The routes will remain closed until further notice," it added.
According to Eurocontrol's information, the doomed plane was flying at a level known as "330", or approximately 10,000 metres or 33,000 feet, when it disappeared from radar screens.
The route itself had been closed to level "320" but was cleared for those flying at the Malaysian plane's altitude.
In Paris, a statement by junior transport minister Frederic Cuvillier said French carriers should "avoid Ukraine's air space as long as the reasons behind this catastrophe are not known".
The Boeing 777 dropped off the radar at around 1415 GMT and crashed in a border region held by pro-Russian separatists.
Ukrainian President Petro Poroshenko pointedly called the disaster a "terrorist act", and major airlines quickly announced plans to route planes away from the area.
Air France said it decided "to no longer fly over eastern Ukraine as soon as it heard of the event," and Alitalia had done the same.
A spokeswoman for German flag carrier Lufthansa told AFP it also chose to immediately make a "wide detour" around the region because "our passenger's safety is our top priority."
Lufthansa's subsidiary Swiss took similar action, and reported that "one flight between Bangkok and Zurich was affected, the flight was rerouted."
In London, a British Department for Transport spokesman confirmed that "flights already airborne are being routed around the area by air traffic control in the region."
US carrier Delta was one of the first non-European carriers to say it too was steering clear "out of an abundance of caution."
"The thoughts and prayers of the entire Delta Air Lines family are with the passengers and crew, and their loved ones, involved in the Malaysia Airlines incident," a statement added.
British Airways was already avoiding Ukrainian airspace, with the exception of one flight a day to the capital Kiev, which is well to the west of the crash zone.
In April, the US Federal Aviation Administration (FAA) declared the troubled Crimean peninsula, southwest of the crash site, a virtual no-fly zone for US airlines and pilots.
A similar no-fly order for European airlines was issued at the time by the European Organisation for the Safety of Air Navigation, the official name of Eurocontrol.