At least two people were killed and several others injured on Monday when a car plowed into a lunch-hour crowd in the southwestern German city of Mannheim.
Police quickly arrested the driver, a German citizen, 40, and believe he acted alone.
Authorities said the suspect was taken to the hospital soon after his arrest.
They declined to say how many people were injured, nor did they confirm whether they suspect the attack was intentional.
Witnesses at the scene described chaos as the vehicle sped through a pedestrian-only area, striking bystanders who had ventured outside to take advantage of unseasonably warm weather.
“This is a terrible incident that has shaken our city,” said Mannheim Mayor Peter Kurz in a brief statement.
Although he did not provide additional details about the driver, Kurz urged residents to remain calm and follow instructions from law enforcement.
Police requested that people avoid the city centre as officers cordoned off the area to begin their investigation.
Thomas Strobl, the interior minister for the state of Baden-Wurttemberg, told the German news agency DPA that the driver’s identity has been confirmed but was not released to the public.
Strobl said that authorities believe the man was the sole perpetrator.
The attack occurred around 12:15 p.m. local time in a busy section of Mannheim’s core, close to a landmark water tower and roughly 700 yards from the city’s Paradeplatz.
Moments later, a crumpled vehicle was seen surrounded by a heavy police presence, with debris scattered along its path.
This latest incident has renewed fears in a country already on edge following several recent vehicle-ramming attacks.
In February, an Afghan asylum seeker, 24, drove into a union demonstration in Munich, killing a two-year-old child and her mother while wounding dozens more.
In December, a Saudi doctor living in Germany for more than a decade was accused of driving his car into a Christmas market in Magdeburg, resulting in six deaths and hundreds of injuries.
Such attacks involving both foreign-born residents and German citizens have sparked debates about domestic security and immigration policy.
In last month’s national elections, the Alternative for Germany Party made its strongest showing yet in part by concerns over public safety.
Officials said additional law enforcement resources have been dedicated to high-risk public events and major urban centres.
Mannheim, with a population of about 320,000, was in the headlines last year when an Afghan citizen fatally stabbed a police officer who tried to intervene at a far-right protest.
Monday’s tragedy prompted the nearby city of Heidelberg to cancel its carnival celebrations scheduled for Tuesday.
“This is the second time within a year that our neighbouring city has suffered such a terrible act of violence,” said Heidelberg Mayor Eckart Würzner.
“In a situation like this, it was inconceivable for us to celebrate a happy carnival parade.”
Authorities continue to investigate how and why this deadly crash happened.