A baby is among five people who have died after a car drove into a pedestrian zone in the German city of Trier on Tuesday.
Police and rescue crews responded to the incident, which has left 15 others injured, at 2pm local time and authorities have told people to avoid the city centre.
The driver, identified as a 51-year-old man from the area, was arrested and the vehicle was impounded, Trier police tweeted.
The suspect, whose name was not released in line with German privacy laws, had no fixed address and had been living in recent days in the Land Rover that a friend had loaned him.
Prosecutor Peter Fritzen, who is heading the investigation, said the car was used in the attack.
He was being interrogated by police and was to undergo a psychiatric examination, Mr Fritzen said, adding that a doctor had recently reached the preliminary conclusion the man could be suffering from mental illness.
“We have no indication that there was any kind of a terrorist, political or religious motive that could have played a role,” he told reporters.
The suspect had also consumed a “not insignificant” quantity of alcohol before the incident and was well above the legal limit, he added.
Police said the driver appeared to have ploughed into pedestrians indiscriminately as he drove through the city centre shortly before 2pm.
ITV News Global Security Editor Rohit Kachroo explains what happened in the attack in Germany
Four people were still in a life-threatening condition in hospital and five others suffered serious injuries, while another six had less serious injuries, state Interior Minister Roger Lewentz said.
The others killed were identified as a 25-year-old woman and a 45-year-old man from Trier; the baby’s mother was among those in hospital. Police said the oldest victim was aged 73.
Mayor Wolfram Leibe, who was brought to tears during the day talking about the horrific scene, said it was difficult to come to grips with what had happened.
“I can’t understand how someone gets the idea to drive through the city centre with an SUV to kill people,” he said.
“Kill people - a baby, nine months old to a woman 72 years old; what did these people do? They just wanted to go to the city, shop, and now they are dead.”
The area was being kept shut down until at least Wednesday morning for police to collect evidence, but there was no longer any danger, Mr Leibe said.
Mr Lewentz commended security forces on their reaction, saying that they had located the car, which had stopped at the side of the street, and taken the suspect into custody within four minutes of receiving the first call.
The driver, who was alone in the car, resisted arrest but was overpowered by police, authorities said.
Rhineland-Palatinate state governor Malu Dreyer, who comes from Trier, condemned it as a “brutal act.” “It was a really, really terrible day for my hometown,” Mr Dreyer told reporters after visiting the scene.
Trier is located in southwest Germany around 200 kilometres (120 miles) west of Frankfurt, and near the border with Luxembourg.
The city of about 110,000 people is known for its Roman gate, the Porta Nigra, which is near the scene of the crash, and as the birthplace of Karl Marx.
In February this year 35 people, including 18 children, were hospitalised after a car drove into crowds at a carnival in the German town of Volkmarsen, east of Dusseldorf.