Berlin airports will close as of 0900 GMT Wednesday because of danger posed by ash pouring from an Icelandic volcano, Germany air safety officials announced.
The leading German airline, Lufthansa, had earlier said it expected to cancel about 150 flights Wednesday because of the ash cloud which on Tuesday had forced the closure of Northern Ireland and Scottish air space.
Operations at Tegel and Shoenefeld airports would halt operations from 11:00 am (0900 GMT), air safety officials said.
In Hamburg, the country's second biggest city, there had been no take-offs or landings since 6:00 am (0400 GMT), an airport spokesman told AFP.
He was unable to say how many of the airport's 453 daily flights would be affected however.
In Bremen, another northern German port, traffic was halted since 05:00 am (0300 GMT) and service by the German flag carrier Lufthansa was cancelled until 04:00 pm (1400 GMT), an airport spokesman said.
Low-cost airline Ryanair had done the same until 11:00 am (0900 GMT), he added. Bremen normally sees around 100 flights per day.
German Transport Minister Peter Ramsauer told public television ARD the situation was expected to improve later in the day.
"Security is the top priority but we can say that the situation will get better later today," Ramsauer said.
Major German hubs in Frankfurt and Munich have not been affected, but Lufthansa expects to cancel about 150 flights on Wednesday to cities that lie in ash clouds' paths, a spokesman told AFP.
Poland and Scandinavian countries were also expected to be affected.
The most active volcano in Iceland began an eruption on Saturday, its most violent in at least a century.
The cloud is the second in barely a year from an Icelandic volcano to disrupt air traffic.