German police said on Tuesday they were treating as "a probable terrorist attack" the killing of 12 people when a speeding lorry cut a bloody swathe through a Berlin Christmas market.
At least 48 more were wounded when the truck tore through the crowd Monday, smashing wooden stalls and crushing victims, in scenes reminiscent of July's deadly attack in the French Riviera city of Nice.
Images showed the mangled truck with its windscreen smashed and a trail of destruction in its wake, with Christmas trees toppled on their side and festive stalls obliterated into splinters.
One of the survivors, Australian Trisha O'Neill, recalled the horror of "this huge black truck speeding through the markets crushing so many people", with "blood and bodies everywhere".
"It wasn't an accident," said another visitor, Briton Emma Rushton, who was enjoying a glass of mulled wine when the festive scene was shattered by a loud crash and screams.
"We heard a really loud bang and saw some of the Christmas lights to our left starting to be pulled down," she told Sky news.
"Then we saw the articulated vehicle going through people and through the stalls and just pulling everything down and then everything went dark."
Police detained the man believed to have deliberately mowed the Scania truck loaded with steel beams for 80 metres (yards) into the popular tourist spot near the capital's iconic Kaiser Wilhelm Memorial Church.
The suspect was an asylum seeker believed to be from Pakistan or Afghanistan who arrived in Germany via the so-called Balkans route in February, according to unnamed security sources cited by DPA news agency.
Local newspapers said that, after the truck driver left the cabin, a man followed him on foot and used his mobile phone to stay in touch with police, who arrested him about two kilometres away near Berlin's Victory Column.
Refugee Shelter Raid
The suspect was believed to have stayed in a Berlin refugee shelter, DPA reported.
Overnight, police commandos raided Berlin's largest such shelter, a hangar of the disused Nazi-era Tempelhof airport, famous because of the Cold War-era Berlin airlift, public broadcaster ZDF reported.
The daily Tagesspiegel said the man behind the wheel was known to police but for minor crimes, not links to terrorism.
A Polish man, thought to have been the truck's registered driver, was found dead on the passenger seat, and police said he had not steered the vehicle.
The Polish owner of the lorry, Ariel Zurawski, had Monday confirmed his driver was missing, telling AFP: "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," he said.
Lukasz Wasik of the same company said contact was lost with the 37-year-old at around 3:00 pm (14.00 GMT).
Wasik said GPS data indicated that the truck was later started three times — "as if someone was practicing how to drive it" — before it drove off at 7:34 pm local time.
'We Mourn the dead'
World leaders expressed shock at the latest attack to hit Europe, as social media users shared their grief on Twitter using the hashtag #prayforberlin.
Chancellor Angela Merkel's spokesperson Steffen Seibert tweeted that "we mourn the dead and hope that the many people injured can be helped," while President Joachim Gauck called it "a terrible evening for Berlin and our country".
German flags flew at half-mast Tuesday and the church near the attack was planning a memorial service later Tuesday.
The suspected attack meant "our worst fears have come true," said conservative lawmaker Stephan Mayer, who added that security will have to be reviewed for a all of Germany's Christmas markets and asked "whether they can take place at all."
More eyewitnesses meanwhile came forward to recall the horrific scenes.
One British visitor, Mike Fox from Birmingham, told how he helped rescue people trapped under collapsed market stalls.
"I saw one guy being dragged away with blood on his face. I helped several other people lift the side of one of the stalls up so that they could pull two other people from underneath."
Europe has been on high alert for most of 2016, with jihadist-style attacks striking Paris and Brussels, while Germany has been hit by several assaults claimed by the "Islamic State" group and carried out by presumed asylum-seekers.
An axe rampage on a train in Bavaria state in July wounded five people, and a suicide bombing left 15 people injured in the same state six days later.
The arrival of 890,000 refugees last year has polarised Germany, with critics calling the influx a serious security threat.
Marcus Pretzell of the anti-immigration Alternative for Germany party labelled the Christmas market victims "Merkel's dead".
The attack in Berlin comes five months after Tunisian extremist Mohamed Lahouaiej Bouhlel rammed a truck into a crowd on the Nice seafront, killing 86 people.
President Francois Hollande said "the French share in the mourning of the Germans in the face of this tragedy".
The United States condemned an apparent "terrorist attack", while the president-elect, Donald Trump, blamed "Islamist terrorists" for a "slaughter" of Christians.