A huge aquarium in Berlin burst, spilling debris, water and hundreds of tropical fish out of the AquaDom tourist attraction in the heart of the German capital early Friday.

Police said parts of the building, which also contains a hotel, cafes and a chocolate store, were damaged as 1 million liters (264,000 gallons) of water poured from the aquarium shortly before 6 a.m. (0500 GMT). Berlin’s fire service said two people were slightly injured.

The company that owns the AquaDom, Union Investment Real Estate, said in a statement Friday afternoon that the reasons for the incident were “still unclear.”

Mayor Franziska Giffey said the tank had unleashed a “veritable tsunami” of water but the early morning timing had prevented far more injuries.

“Despite all the destruction, we were still very lucky,” she said. “We would have had terrible human damage” had the aquarium burst even an hour later, once more people were awake and in the hotel and the surrounding area, she said.

The website of the AquaDom described it as the biggest cylindrical tank in the world at 25 meters tall (82 feet tall), although Union Investment Real Estate clarified Friday that the tank portion of the attraction had a height of 14 meters (46 feet).

There was speculation freezing temperatures that got down to minus 10 degrees Celsius (14 degrees Fahrenheit) overnight caused a crack in the acrylic glass tank, which then exploded under the weight of the water. Police said they found no evidence of a malicious act.

Nearly all of the 1,500 fish that were inside at the time of the rupture died, the Berlin Mitte district government confirmed via Twitter, adding “a few fish at the bottom of the tank” could still be saved. Among the 80 types of fish it housed were blue tang and clownfish, two colorful species known from the popular animated movie “Finding Nemo.”

Veterinarians, fire service officers and other officials spent the afternoon working to rescue 400 to 500 smaller fish from a separate set of aquariums housed under the hotel lobby. Without electricity, their tanks were not receiving the necessary oxygen for them to survive, officials said. They were evacuated to other tanks in the neighboring Sea Life aquarium that were unaffected.

“It’s a great tragedy that for 1,500 fish there was no chance of survival,” said Almut Neumann, a city official in charge of environmental issues for Berlin’s Mitte district. “The focus in the afternoon was clearly on saving the fish in the remaining tanks.”

Various organizations, including the Berlin Zoo, offered to take in the surviving fish.

Aquarium operator Sea Life said it was saddened by the incident and trying to get more information from the owners of the AquaDom. It said what happened with the AquaDom was “unique and unprecedented” and that Sea Life’s exhibits were not in danger of similar damage.

Sea Life Berlin is located in the same building and visitors can tour it and the AquaDom on a single ticket.

About 300 guests and employees had to be evacuated from the hotel surrounding the aquarium, police said.

Sandra Weeser, a German lawmaker who was staying in the hotel, said she was woken up by a large bang and thought there might have been an earthquake.

“There are shards (of glass) everywhere. The furniture, everything has been flooded with water,” she said. “It looks a bit like a war zone.”

Police said a Lindt chocolate store and several restaurants in the same building complex, as well as an underground parking garage next to the hotel, sustained damage. A fire service spokesman said building safety experts were assessing the extent to which the hotel had sustained structural damage.

Hours after the incident, trucks began clearing away the debris that had spilled out onto the street in front of the hotel. Brightly colored Lindt chocolate wrappers were scattered in front of the building where the chocolate shop was damaged. A small crowd of tourists and onlookers snapped photos from behind the police line across the street.

Animal rights group PETA tweeted Friday that the aquarium became a “death trap” for the fish housed in it. “This man-made tragedy shows that aquariums are not a safe place for fish and other marine life,” the group wrote.

The aquarium, which was last modernized in 2020, is a major tourist magnet in Berlin. The 10-minute elevator ride through the tropical tank was one of the highlights of the attraction.

Iva Yudinski, a tourist from Israel who was staying at the hotel, said she was shocked by the incident

“Just yesterday we watched it and we were so amazed (by) its beauty,” she said. “Suddenly it’s all gone. Everything is a mess, a total mess.”