German authorities scrambled Tuesday to determine the motives of a man who ploughed his car into a carnival procession, injuring dozens and further unsettling a country rocked by a fatal mass shooting last week.

In an afternoon statement, police said the number injured had now reached around 60 and asked those hurt in the incident or with possible evidence to come forward.

The youngest of the casualties was only two years old and 20 of those injured were children. The oldest person injured was 85.

Investigators said the 29-year-old German driver had not been drunk at the time of the incident on Monday, but could not yet rule out that he was under the influence of drugs, national news agency DPA reported.

The suspect has still not been questioned because of his own injuries, a police spokesman told reporters near the scene of the incident in Hessian town Volkmarsen.

The incident came just days after a gunman with suspected racist motives killed nine people with migrant backgrounds in Hanau, also in western Hesse state, prompting fears of a repeat attack.

Officials cancelled all carnival parades across the state on Monday, while a children's procession was called off Tuesday in state capital Wiesbaden.

But authorities have stopped short of calling the incident an attack until they know more about the driver's motives.

"I saw him drive off, he looked as if he was on drugs and said 'soon I'll be in the papers'," a neighbour of the suspect told German broadcaster RTL.

Nevertheless, prosecutors in Frankfurt have opened an investigation into suspected attempted homicide. They feel the driver deliberately drove at the crowd with the intention of killing.

Prosecutors said they had also arrested a second person who filmed the car rampage, citing a privacy law against gawkers.

The latest incident prompted fears of a repeat attack with carnivals and parades in Germany's Hesse state cancelled
The latest incident prompted fears of a repeat attack with carnivals and parades in Germany's Hesse state cancelled AFP / INA FASSBENDER

Eyewitnesses described how the man ploughed his silver Mercedes at high speed through a barrier and into crowds at the traditional "Rose Monday" parade in Volkmarsen, a small town in Hesse state.

"My wife called me and I ran out there straight away. I saw my daughter lying bleeding on the ground," 33-year-old Sven Hirdler told mass-market newspaper Bild.

Hirdler's four-year-old child Emilia escaped with relatively light injuries and a concussion.

On Tuesday morning, carnival floats and balloons were still in place around Volkmarsen, while emergency vehicles remained at the scene as the perpetrator's car was hauled away.

Hessian police said that of the injured, 35 remained in hospital while 17 had already returned home.

As in many parts of the country, residents in Volkmarsen were celebrating Rose Monday, a highlight of annual carnival festivities that sees adults and children dress up and attend parades where people play music and throw candies from floats.

The party, traditionally celebrated mostly in western Germany, had been a welcome relief for a country shaken by last Wednesday's deadly Hanau shootings.

The rampage fuelled concerns over the country's increasingly emboldened far-right scene, after a pro-migrant politician was murdered in June and an anti-Semitic attack on a synagogue left two dead in the city of Halle last October.

The sight of a car ploughing through crowds recalled Germany's deadliest terror attack in recent history, when a jihadist drove his truck into a crowded Berlin Christmas market, killing 12 people in December 2016.

The attacker, a failed Tunisian asylum seeker, had pledged allegiance to the Islamic State group.

After the Hanau shootings, Interior Minister Horst Seehofer on Friday vowed to put more police at mosques, train stations, airports and borders.