German interior minister Thomas de Maiziere has said the fact the air passengers in the EU's borderless region only need to present a ticket to board a plane is a "huge security problem".

He told the Bild newspaper that experts investigating last week's Germanwings plane crash that killed 150 passengers were first confronted with the problem of not knowing exactly who was on the plane.

Student or retired? Then this plan is for you.

"After the attack we checked whether the passengers and crew were known troublemakers because we wanted to know if it was a terrorist attack. But we realised that it was not immediately clear who was on the plane."

"If a passenger gives their ticket to someone else, only the name of first passenger is detected. This is a huge security problem and we have to seriously consider whether it can remain like this in the future," said de Maiziere.

He said he would examine whether carrying and showing ID for flights should be obligatory in the Schengen area - in the 26 European countries that belong to the area, air passengers' ID are not systematically checked.

"A flight is not comparable to a train or bus journey for which tickets are issued anonymously. In my opinion, we need to know for security reasons who is really on board a flight," said de Maiziere.

He also said there should be a better of exchange of information about air passengers with authorities from non-EU states.

In future, it should be possible that the names of dangerous or "potentially dangerous" people from outside Europe and "especially from crisis regions" be exchanged.

The Schengen agreement - applying to most EU countries as well as Norway, Switzerland, Liechtenstein and Iceland - is seen as one of the cornerstones of EU integration, relying on solidarity and trust between member states.

However its rules have been called into question on several occasions in past years - most recently following the terrorist attacks in January in Paris.

Meanwhile de Maiziere also told Bild that French and German experts are looking into whether a door protection mechanism - whereby the pilot can lock the door to the cockpit - should be abolished again.

The security mechanism was introduced after the September 2001 terrorist attacks in New York and Washington which saw hijackers take over command of the cockpits.

But in last week's crash it emerged that the co-pilot locked the cockpit door after the captain left to use the bathroom. The captain was then unable to get back in while the co-pilot deliberately crashed the plane.