A huge fire broke out Thursday in a popular forest in western Berlin next to a police munitions storage site, sending plumes of smoke into the skies and setting off intermittent explosions.
The army sent in a tank aimed at evacuating munitions at the affected storage site as well as remote-controlled de-mining robots, while drones were circling the air to help assess the emergency.
The situation is "extremely extraordinary with munitions," said Berlin fire brigade spokesman Thomas Kirstein, adding that it was "under control and there was no danger for Berliners."
The fire was however expected to last for some time, he said.
Firefighters called to the site in the middle of the night were confronted with intermittent blasts that sent debris flying and hindered their work.
They have so far been able to begin tackling only two of the four hotspots across the affected area of 15,000 square metres (161,500 square feet), as explosions at the munitions store were still rocking the area.
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No one has been hurt by the fires, which came on a day when a new heatwave was due to envelop Germany.
Officials have built a security cordon to allow firefighters to start working around a kilometre from the ammunition storage zone.
The store holds munitions uncovered by police, but also unexploded World War 2-era ordnance which is regularly dug up during construction works.
Police said they were investigating what set off the fire.
Authorities appealed for the public to avoid the forest, popular with both locals and tourists, as several regional rail lines have been halted.
But authorities said no firefighting choppers were available as they were already in use to calm forest fires in eastern Germany.
The German capital is rarely hit by forest fires, even though its 29,000 hectares of forests make it one of the greenest cities in the world.
Brandenburg, the region surrounding Berlin, as well as parts of eastern Germany have for days been battling forest fires.
Scientists say climate change is making heatwaves around the world more frequent and more intense, which increases the risk of fires.
Temperatures are expected to climb as high as 40 degrees Celsius (104 degrees Fahrenheit) across parts of Germany on Thursday. In Berlin, they are predicted to reach 38C.
After a scorching Thursday, heavy thunderstorms are due to sweep into the country from the west on Friday, the German weather service said.
A cold front is predicted to bring temperatures down by more than 10 degrees overnight in western Germany, falling to around 20-25 degrees on Friday.