Police have confirmed the truck that ploughed into a Christmas market in Berlin was a deliberate attack.
Twelve people have been killed and 48 people have been injured, some severely.
A police spokesperson confirmed it was an apparent terrorist attack, saying they will put all possible resources into the investigation.
German daily newspaper Die Welt and news agency DPA also reported the driver came to Germany as a refugee in February and had used several different names, which was making his identification difficult.
- Are you in Berlin? Get in touch: firstname.lastname@example.org
Police have confirmed one man was found dead in the truck; however, he was a Polish citizen and not the driver.
The truck has Polish number plates and is believed to have been stolen from a construction site.
One suspect, believed to be the driver, fled the scene shortly after. Police have since arrested the man.
The truck careered into the Berlin market at what would have been one of the most crowded times for the Christmas market, when adults and children would be gathering in the traditional cluster of wooden huts that sell food and Christmas goods.
"I heard a big noise and then I moved on the Christmas market and saw much chaos...many injured people," Jan Hollitzer, deputy editor in chief of Berliner Morgenpost, told CNN. "It was really traumatic."
Police believe the truck used in the attack was stolen from Poland and driven to the German capital.
German broadcaster ZDF reported the alleged driver was seen fleeing from the scene. Police have since said one suspect is in custody, while a second died in the truck.
Witnesses told CNN there was "no sign" the massive truck intended to slow down as it drove through Breitscheidplatz, a public square in the city's west.
One witness said on Twitter the truck was going about 65km/h, and there "is no road nearby". Another said people had been "crushed".
Julian Reichelt, editor in chief of Bild Berlin, said the security operation that followed was "a reminder of what we have seen in Nice".
Video of the attack's aftermath shot by a Berlin newspaper showed destroyed stalls, and police sirens could be heard. Armed police are guarding the scene.
German Chancellor Angela Merkel, through a spokesman, said she was "in mourning for the dead and hope that the many injured can get help".
Facebook set up a Safety Check page following the incident, allowing users to tell friends they are safe.
There are 360 New Zealanders registered with the Ministry of Foreign Affairs and Trade's SafeTravel service. It's not known yet if any were caught up in the attack - the New Zealand embassy is talking to local authorities, trying to find out.
Kiwis in Berlin are advised to "stay away from the immediate vicinity, follow the advice of the local authorities, monitor the media to keep up to date with developments and get in touch with family in New Zealand to confirm their wellbeing".
If a friend or loved one is in Berlin and you are unable to reach them, MFAT can be reached on (04) 439 8000.
Christmas markets are very popular in Germany, and it's likely there would have been thousands of people at Breitscheidplatz.
There has been heightened security this festive season following recent terror attacks in Europe.
In July, 86 people were killed when a cargo track rammed into crowds celebrating Bastille Day in Nice, France. Islamic State claimed that attack.
Reuters / Newshub.