Here is what we know of the event reminiscent of the horrific scenes in July when a truck drove into a crowd in the French Riviera city of Nice.
Around 8 pm (1900 GMT) a lorry drove for up to 80 metres (yards) into a busy Christmas market frequented by locals and tourists.
The deadly event took place in the shadow of the Kaiser Wilhelm Memorial Church whose damage in a World War II bombing raid has been preserved as a reminder of the horrors of war.
12 killed as lorry ploughs into Berlin Christmas market
The man who was apparently driving the Polish-registered truck was detained, a police spokesperson said without giving further details.
Police said a passenger was found dead in the cab of the lorry and later identified him as a Polish national. The identities of the 11 other victims are not yet known.
Police suspect a terror attack, with Interior Minister Thomas de Maiziere saying there are "many reasons" to believe the killings were deliberate. The Federal prosecutor's office for terrorism cases has taken over the investigation.
The minister said on television that security services had "no indication" that Christmas markets could be the target of assaults if Jihadist groups wanted to attack Germany.
A suspect was arrested some two kilometres (one mile) from the scene, police said, with de Maiziere adding he was likely to have been behind the events. Authorities have yet to comment on the man's identity.
Security sources cited by DPA news agency said that the man behind the wheel was an asylum seeker from Afghanistan or Pakistan who arrived in Germany in February. The daily Tagesspiegel newspaper said the man was known to police but for minor crimes, not links to terrorism.
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The Polish owner of the lorry confirmed his driver was missing.
"We haven't heard from him since this afternoon. We don't know what happened to him. He's my cousin, I've known him since I was a kid. I can vouch for him," transport company owner Ariel Zurawski told AFP.
The company's transport manager, Lukasz Wasik, said the driver was 37 years old and had been transporting Thyssen steel products from Italy to Berlin.
"The company where he was supposed to unload the products in Berlin was not able to receive them and told him to return on Tuesday morning. They told him to wait in Berlin somewhere," Wasik told AFP.
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