A “probable terrorist attack” in German capital Berlin has left 12 people dead and a further 48 injured.
A suspect is believed to have deliberately driven a lorry into a crowded Christmas market in the centre of the city.
The driver of the lorry has been detained, with reports suggesting he is an Afghan or Pakistani asylum seeker.
He arrived in Germany in February as a refugee, the DPA news agency said earlier.
The incident happened at a market at Breitscheidplatz, close to the Kurfuerstendamm, the main shopping street in the west of the city.
“All police measures related to the suspected terrorist attack at Breitscheidplatz are progressing at full steam and with the necessary diligence,” Berlin Police said on Twitter.
The truck veered into the market at 20:14 local time, at the height of festivities.
It crashed, loaded with steel beams, through wooden huts packed with tourists and locals.
The driver was seized after leaving his truck and fleeing on foot.
Police confirmed that a passenger, a Polish national, was found dead in the lorry.
There are fears he may have been the original driver of the vehicle, possibly killed during a hijacking.
American travellers were last month warned by the department of state over the heightened risk of terrorist attacks throughout Europe, particularly during the holiday season.
US citizens were urged to exercise caution at holiday festivals, events, and outdoor markets.
Credible information from the US indicates so-called Islamic State, al-Qa’ida, and their affiliates continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events.
“US citizens should also be alert to the possibility that extremist sympathizers or self-radicalized extremists may conduct attacks during this period with little or no warning,” warned the state department.
At the same time, the British Foreign & Commonwealth Office warned there is a high threat from terrorism in Germany.
The German government has announced that increased security has been put in place as a precaution at public buildings, major events, transport hubs and large public gatherings.
“You should remain vigilant and follow the advice of local authorities,” warned the FCO.
Around two million British visitors arrive in Germany each year.