General view of the interior of the cockpit of an A320 aircraft belonging to Jetstar Asia airways, at Singapore airport January 31, 2015.[Photo/Agencies]

BERLIN/PARIS - Airlines rushed on Thursday to change their rules so as to require a second crew member in the cockpit at all times, hours after French prosecutors suggested a co-pilot who barricaded himself alone at the controls of a jetliner had crashed it on purpose.

The United States already requires two crew members to be in the cabin at all times, but many other countries do not, allowing pilots to leave the flight deck, for example to use the toilet, as long as one pilot is at the controls.

That is precisely what French prosecutors suspect happened on the Germanwings flight on Tuesday. They say Andreas Lubitz, 27, locked the captain out and appears to have set the controls to crash into a mountain, killing all 150 people on board.

Airlines including Norwegian Air Shuttle, Britain's easyJet, Air Canada, Air New Zealand and Air Berlin all said within hours that they had introduced a requirement that two crew members be in the cockpit at all times.

Canada said it would immediately impose such a rule on all its airlines while those that already had such rules in place, including Ryanair, rushed to reassure customers.

Among the companies that did not announce such a policy change was Germanwings parent Lufthansa, whose CEO Carsten Spohr said he believed it was unnecessary.

"I don't see any need to change our procedures here," Spohr told journalists. "It was a one-off case. But we will look at it with the various experts at Lufthansa and the authorities. We shouldn't lose ourselves in short-term measures."

His comments drew criticism on Twitter, with some people demanding the airline introduce the two person-rule.