Due to ash from an Icelandic volcano entering German airspace, no planes were permitted to take off or land at several northern German airports Wednesday morning.

Flights at City Airport Bremen were grounded starting at 5 a.m. local time, and the same flight ban was imposed on Hamburg Airport one hour later. The capital's airports - Tegel and Schönefeld - were also shut down.

Germany's flight safety authority (DFS) said the Bremen and Hamburg airports reopened before noon, and Berlin opened around 2 p.m. The German weather service said the ash concentration in the air was no longer critical.

Airlines and airports said the closures affected hundreds of flights and tens of thousands of passengers.

Since Sunday, the ash from Iceland's erupting Grimsvotn volcano has swept across Britain and Northern Ireland, causing the cancellation of hundreds of flights, especially to and from Scotland. On Tuesday, the ash cloud reached Scandinavia where it caused minor air traffic disruptions in Norway and closed a small part of Denmark's airspace.

Repeat of 2010 chaos not expected

Iceland's Meteorological Office said activity at the volcano had slowed. The ash plume dropped overnight Monday from its peak of 20 kilometers (12.5 miles) to less than five kilometers in altitude.

The EU Commission in Brussels also said Tuesday it is not expecting a repeat of the chaos last year caused by the eruption of the Eyjafjallajokull volcano, which grounded more than 100,000 flights and left 8 million passengers stranded.

"We do not at this stage anticipate widespread airspace closure and prolonged disruption like we saw last year," Siim Kallas, Europe's transport commissioner, told a news conference.

Nevertheless, "we are still looking at a very challenging week for passengers and for the airlines," Kallas warned.

Safety precautions or overreaction?

Conflicts continue between EU states, European authorities and airline companies over how to apply new safety rules for flying when there are large amounts of ash in the air.

German authorities are taking a tough stance. The German Transport Ministry has told pilots that aircraft will be refused clearance if ash concentrations exceed 2 milligrams, which is considered low.

The Volcanic Ash Advisor Centre in London has forecasted that the cloud in Germany will have ash concentrations of between 0.2 and 2 milligrams.

Irish budget airline Ryanair was highly critical of decisions by regulators to close Europe's skies during last year's eruption.

On Tuesday, it flew a plane through Scottish airspace which regulators say had a "high ash concentration," in a bid to show there was no danger from the volcanic eruption.

The German government however insists on a 2 milligram maximum limit. It said if airlines believe it is safe to fly above the limit, then they must provide hard scientific proof and not rely on local safety audits.

Author: Mark Hallam, Gabriel Borrud (AFP, dpa, Reuters)

Editor: Martin Kuebler