Around 100 emergency responders rushed to the site, a leisure complex that houses a Radisson hotel and a museum as well as what Sea Life Berlin said was the world's largest freestanding cylindrical aquarium at 14 metres (46ft) in height.

"It felt like an earthquake" said Naz Masraff, who had been staying at the hotel.

Another hotel guest, Sandra Weeser, spoke of chaos.

"The whole aquarium burst and what’s left is total devastation. Lots of dead fish, debris," she told Reuters.

The 1,500 fish from the aquarium died, said a spokesperson for Union Investment, which manages the real estate fund that owns the property.

Efforts are underway to rescue fish from several smaller tanks that were near the AquaDom and that escaped destruction but have been subjected to power cuts in the building, he said.

A spokesperson for the fire brigade told Reuters it was still unclear what had caused the AquaDom aquarium to burst.

TRAGEDY AVERTED?

It was fortunate that the accident happened so early in the morning, when there was hardly anybody in the immediate vicinity, Berlin mayor Franziska Giffey was quoted as saying.

"If this hadn't happened at 5.45 am but even just one hour later, then we would probably have had terrible human loss to report," broadcaster RBB cited Giffey as saying.

Two people, including a hotel employee, were injured by splinters of glass, and emergency services asked around 350 hotel guests to pack their belongings and leave amid concerns that there could be structural damage.

Buses were sent to provide shelter for the hotel guests, police said, as outside temperatures in Berlin in the morning hovered around -7 degrees Celsius (19.4°F).

Radisson told its Radisson Rewards loyalty club members in an e-mail that the Radisson Collection Hotel Berlin was closed until further notice.

Sea Life Berlin said in a statement its team was shocked by the incident and was trying to obtain more information from the owners of the AquaDom about what had caused the incident.

The company, which had offered glass elevator rides through the AquaDom aquarium, said it would also remain closed until further notice.

Emergency services shut a major road next to the complex that leads from Alexanderplatz toward the Brandenburg Gate due to the large volume of water that had flooded out of the building.

The aquarium was last refurbished in 2020, according to the website of the DomAquaree complex. During the upgrading work, all the water was drained from the tank and the fish were moved to aquariums in the basement of the building, where there is a breeding care facility for the fish, it said.