German airports have been hit by a nationwide IT outage affecting police systems at border control, causing disruption and longer immigration queues for passengers from outside the European Union's Schengen travel zone.

"There is currently a nationwide IT disruption," a federal police spokesperson said on Friday by phone, forcing officers to manually process passengers arriving from outside the passport-free Schengen area.

The cause was not immediately known. The outage caused queues of people waiting at border control at several German airports, including Frankfurt, the country's busiest.

Berlin airport confirmed longer waiting times at immigration for non-Schengen passengers.

"We can confirm that since around 2 p.m. (1300 GMT) today, there have been disruptions to border control for flights to and from the non-Schengen area," said a spokesperson for Dusseldorf airport, saying passengers were being provided with water.

The regional public broadcaster WDR reported that passengers were waiting for two hours at immigration while others were being kept on the plane.