The incident only came to light early on Saturday morning when a police officer noticed that a part of the barriers around the parliament building had disappeared, and followed clues which led to the water.

“The officers followed car tracks in the direction of the Spree river bank and saw that a fence along the promenade was also smashed,” a police spokesman told daily Der Tagesspiegel on Sunday.

The fact that the tracks led into the water prompted the officers to call the fire brigade, who had to assume there could be people in the car and sent a team of divers to find the vehicle.

“The vehicle was empty, but we did not know whether those inside had managed to rescue themselves,” a spokesman for the fire brigade said.

A check of the license plates led police to the 20-year-old owner, who had initially registered it as stolen, before admitting that he and a 17-year-old girlfriend had been in it during the crash.

He said they were driving at high speed along the cul de sac by the Paul Löbe Haus next to the Reichstag when he lost control, smashed through the barrier and fence, and flew around 10 metres onto the promenade before crashing into the river.

They both managed to get out of the car and swim to the side before walking to nearby Friedrichstrasse and checking into a hotel to change clothes. Police investigating the case found wet clothes on the balcony of the hotel room.

Apart from a number of bruises, the couple were uninjured. Police and fire spokesmen said they were lucky to be alive.

The driver was tested for alcohol, with a result of 0.8 promille, over the 0.5 promille limit for drivers. He would not make a statement about the time of the accident or the exact details of how it happened.

“The car must have been going at least 100 kilometres an hour,” said fire department spokesperson Jens-Peter Wilken.

Questions are now being asked about how no-one noticed the crash until 6 am, since the Reichstag is one of the most monitored and protected places in the capital.

Der Tagesspiegel said several police units are supposed to be active in the governmental quarter – the Berlin state police, plain-clothes detectives of the state protection unit, federal police, security details from the federal police and members of the parliamentary police which are specifically responsible for the Reichstag and the Paul-Löbe Haus, where much parliamentary work is conducted.

Berlin MP Stefanie Volgelsang said she found the entire incident odd.

“The police officers in the Paul-Löbe Haus are there 24 hours a day. They must have heard something,” she said, although she admitted that due to the parliamentary summer break less security was needed.