A giant aquarium burst in Berlin on Friday, sending a "tsunami" of water and 1,500 tropical fish gushing into a hotel lobby and spewing debris onto a nearby street.

It remains unclear what caused the 14-metre (46-foot) high, cylindrical AquaDom aquarium to explode at around 5:50 am (0450 GMT), police said.

"A million litres of water and all the fish inside spilled onto the ground floor" of the hotel complex housing the aquarium, a spokesman for the Berlin fire department told AFP.

Guests at the Radisson Blu hotel reported being woken up by a loud bang and the feeling of a small earthquake, before seeing the destroyed aquarium and wrecked hotel lobby.

Two people suffered light injuries from glass splinters and were taken to hospital and all the fish died.

"It was a full-on tsunami," said Berlin Mayor Franziska Giffey, adding that it was pure luck the incident had happened in the early morning when very few people were around.

"Despite the terrible destruction we're seeing, we're lucky people weren't seriously injured," she told reporters.

The 1,500 fish in the tank however "could not be saved", Giffey added.

More than 100 emergency workers were at the scene, which was scattered with glass and other debris.

The cylindrical AquaDom, which opened in 2004, has long been a popular tourist attraction in the German capital.

It is located in the foyer of a Radisson Blu hotel and had a clear-walled elevator built inside to be used by visitors to the Sea Life leisure complex.

According to the Sea Life website, the AquaDom is the largest cylindrical, freestanding aquarium in the world.

Hotel guest Claudia Gonzales said she "jolted out of bed" when the aquarium burst.

"It sounded almost like a firework but the hotel actually shook inside," she told AFP.

- 'Frozen parrot fish' -

Berlin police said water had "massively" leaked onto the adjoining Karl Liebknecht Street, forcing the partial closure of the major traffic artery. Tram service was also suspended.

The area around the hotel remained sealed off by the early afternoon.

The deluge of water left a path of destruction in its wake, breaking windows and doors and sweeping chairs, tables and plant pots into the street outside the hotel.

Pictures and videos circulating online, apparently from guests staying at the hotel, showed extensive damage to the transparent aquarium, with only the frame still standing.

German lawmaker Sandra Weeser, who was staying at the hotel when the aquarium burst, said she was woken up by "a kind of shockwave".

"There was a slight tremor of the building and my first guess was an earthquake," she told the Berliner Morgenpost newspaper.

The area where the aquarium once stood was now just "dark and wet", she said, recalling how she saw "one of those large parrot fish lying on the ground, frozen".

- Recently renovated -

Around 300 guests were staying at the hotel. They have been evacuated.

The complex that housed the aquarium is also home to the GDR museum, devoted to everyday life in former communist East Germany.

The museum, located in the basement of the complex, suffered serious water damage and will likely remain closed until late February, its director Gordon von Godin told local media.

The Sea Life Berlin centre, which sells tickets for the AquaDom elevator ride and also has its own collection of aquariums nearby, said it too would remain shut "until further notice".

A spokesman stressed that Sea Life Berlin did not own the aquarium nor was it responsible for its maintenance.

"We are trying to get information from the owners of AquaDom," he said in a statement.

The Bild newspaper said the aquarium had only reopened this summer after a two-year renovation that cost around 2.6 million euros ($2.7 million).