BERLIN • A truck ploughed through a crowded Berlin Christmas market on Monday night, turning a scene of festive joy into one of carnage and horror that left 12 people dead and 48 injured.

The driver of a heavily laden black truck smashed into wooden huts serving mulled wine and sausages at the foot of the Kaiser Wilhelm Memorial Church, one of west Berlin's most famous landmarks.

Witnesses said the driver was aiming for people during the rampage, with some victims still trapped under the vehicle when it stopped.

The incident evoked memories of an attack in Nice, France, in July when a Tunisian-born man drove a 19-tonne truck along the beach front, mowing down people who had gathered to watch the fireworks on Bastille Day, killing 86 people. That attack was claimed by the Islamic State in Iraq and Syria.

Police detained a suspect in the Berlin attack, and German Interior Minister Thomas de Maiziere said the arrested man, who denied involvement, was probably from Pakistan and was in the process of applying for asylum.

Police later said he might not be the right man, sparking concern that the real killer could be on the run, and heightening fears among Germans, who have faced several terror attacks this year.

"This is a very difficult day," Chancellor Angela Merkel said.

"Like millions of people in Germany, I am horrified, shocked and deeply saddened by what happened in Berlin."

The attack fuelled immediate demands for a change to Dr Merkel's immigration policies, under which more than a million people fleeing conflict and poverty in the Middle East, Africa and elsewhere have arrived in Germany this year and last.

"We must say that we are in a state of war, although some people, who always only want to see good, do not want to see this," said Interior Minister Klaus Bouillon of the state of Saarland, who is a member of Dr Merkel's Christian Democratic Union (CDU).

Mr Horst Seehofer, leader of the CDU's Bavarian sister party, said: "We owe it to the victims, to those affected and to the whole population to rethink our immigration and security policy and to change it."

The record influx has hit Dr Merkel's ratings as she prepares to run for a fourth term next year, and boosted support for the anti-immigrant Alternative for Germany (AfD). Senior AfD member Marcus Pretzell blamed Dr Merkel on Twitter for the attack .

Newspaper Die Welt said the man behind the wheel had jumped out of the vehicle and run down the street towards the Tiergarten, a vast park in central Berlin. It said several witnesses called the police, including one who chased the suspect while on the phone, constantly updating officials on his whereabouts.

The authorities said a Polish man was found shot dead inside the vehicle, but Mr de Maiziere said no gun had yet been found.

Berlin police are investigating leads that the Polish-owned truck had been stolen from a construction site in Poland.

The Polish driver of the truck had arrived hours earlier in Berlin and spoken to his wife on Monday afternoon, according to his cousin.

When she called again an hour later, there was no answer.

"The phone was just silent, silent. He should have picked up if he was on a break, particularly if his wife was calling," said the cousin, Mr Ariel Zurawski, who is also the boss of the trucking company.

"At 3.45pm, you can see the movement on the GPS (Global Positioning System). The car moved forward and back. As if someone was learning to drive it," Mr Zurawski told Polish public broadcaster TVP Info yesterday. "I knew something was wrong."

At about 8pm on Monday, Berlin time, the lorry was used to attack the Christmas market.

REUTERS, AGENCE FRANCE-PRESSE