Police detained the car's driver and later said he had acted alone, and no broader threat had been seen for the public. The suspect is a 40-year-old German man from the neighbouring state of Rhineland-Palatinate. He did not appear to be politically or religiously motivated, authorities said.
"At this time, we have no indications of an extremist or religious background regarding the specific motivation for the act," Interior Minister of the state of Baden-Wuerttemberg Thomas Strobl told reporters.
"The motivation may rather be rooted in the perpetrator's own personal circumstances. However, this is the subject of ongoing investigations."
Broadcaster SWR reported that the suspect had experienced psychological issues.
People were seen lying on the ground at the scene and at least two were being resuscitated, a witness told Reuters.
There did not appear to be a connection to Germany's carnival celebrations, Strobl said. Those festivities culminated on Rose Monday with a number of parades, although not in Mannheim, which held its main event on Sunday.
Security has been a key concern in Germany following a string of violent attacks in recent weeks, including deadly car rammings in Magdeburg in December and in Munich last month, as well as a stabbing in Mannheim in May 2024.
"The incident—like the terrible acts of the past months—serves as a stark reminder: we must do everything possible to prevent such acts," said Germany's likely next leader Friedrich Merz, whose conservatives won a national election last month.
"Germany must once again become a safe country. We will work with full determination to achieve this."
Police were on high alert for this year's carnival parades after social media accounts linked to the Islamic State militant group called for attacks on the events in Cologne and Nuremberg.
German Interior Minister Nancy Faeser cancelled her attendance at the parade - Germany's biggest - in Cologne on Monday, due to the events in Mannheim.
It is a terrible act, as I have said—a horror in broad daylight," Faeser told reporters, speaking alongside Strobl.
Messages of solidarity arrived from across Europe.
"To all the people of Mannheim, especially to all the relatives of the victims of the attack, to the German people. France is at your side," French President Emmanuel Macron wrote on the social media platform X.
Italy's Prime Minister Giorgia Meloni said "attempts to destabilize democratic nations will not prevail".
Rose Monday, the culmination of the annual carnival season celebrated in Germany's mainly Catholic western and southern regions, features parades of floats that often include comical or satirical references to current affairs.
This year's carnival has included floats featuring US President Donald Trump, Russian President Vladimir Putin, tech billionaire Elon Musk and Ukrainian leader Volodymyr Zelenskiy.
Dressed in traditional jester costumes and sporting colourful makeup, thousands of partygoers danced through the streets of Cologne, Dusseldorf and other cities in western and southern Germany ahead of the fasting season of Lent.
