BERLIN (AP) — A large fire triggered by explosions at an ammunition dump raged Thursday in a major Berlin urban forest on one of the German capital's hottest days so far this year.

A huge cloud of grey smoke hung over the city’s western districts and residents were asked to keep windows and doors shut. A major highway was closed and a train service interrupted, but authorities said no homes or inhabitants were under direct threat.

More than 100 firefighters, dozens of soldiers and police officers were battling the blaze in the Grunewald forest, located in west Berlin.

In addition, army tanks cut corridors into the forest to contain the fire and allow firefighters to get closer to the flames. The army also sent in a remote-controlled robot with four cameras and a grappler that can be used to detect and eliminate ordnance.

Water cannons were also on the scene and firefighters drew water from the nearby Havel river to extinguish the flames.

“The situation is dangerous,” Thomas Kirstein from the Berlin fire department told reporters earlier Thursday.

Massive explosions were heard in the morning from the site where old ammunition from World War II, fireworks and explosive ordnance is stored and controlled explosions are carried out.

Kirstein said it was not clear what had triggered the first explosions at the ammunition dump early Thursday. The site belongs to the Berlin police. It was created in 1950, and before Thursday's explosions around 25 metric tons of fireworks, World War II ammunition and other explosive ordnance was stored there, the German news agency dpa reported. Controlled blasts are scheduled there twice a year for several days at a time.

Kirstein called on residents to stay away from the forest and authorities declared a one-kilometer (more than half a mile) exclusion zone around the ammunition dump. Due to flying debris and the threat of further explosions, the fire department said it could not systematically extinguish the fire as emergency forces were also not allowed to enter the exclusion zone. Firefighters on the scene were initially pouring water on the forest outside the banned area around the ammunition dump trying to prevent the blaze from spreading further.

They were also planning to get aerial images by flying a drone over the ammunition dump to better be able to judge the situation.

“The plan is to get a new situation assessment from the blast site — initially from the air," Kirstein said. According to first estimates an area of 1.5 hectares was burning all around the ammunition dump.

Berlin Mayor Franziska Giffey cut short her vacation to visit the scene and thank the emergency personnel for their efforts. She made clear that no homes or residents were threatened, but also said city authorities needed to seriously talk about moving the ammunition dump out of the vicinity of the city of 3.65 million residents.

The commuter train service to the city's west was partially interrupted and one of the city's most important highways, the Avus, was closed. Homes were not directly threatened by the flames but the fire department warned that the fire could further spread due to the dry conditions of the forest and the exceptional heat expected on Thursday with temperatures of up to 38 degrees Celsius (100 Fahrenheit).

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