Authorities in Germany were investigating what prompted a man to go on the rampage with a knife, killing three women and seriously injuring five other women.

Officials said the suspect, whose rampage was halted when police arrested him, was a 24-year-old Somali immigrant who had had mental health problems in the past. As is the practice in Germany, they did not name him.

Officials assume the suspect was acting alone, but are still investigating whether there was any Islamist motive for the attack, regional Interior Minister Joachim Herrmann told a news conference.

Herrmann cited one witness as saying that before starting his spree the suspect had shouted “Allahu akbar”, an Arabic phrase that means “God is great” and that is often associated with acts of Islamist militancy when used by attackers.

“The indications of radicalisation, in this case Islamism, and of psychological problems do not necessarily rule one another out … this must be the subject of further investigation,” Herrmann said.

The man went into the kitchen department of a store and asked an assistant where the knives were, regional police president Gerhard Kallert said. He seized a knife and stabbed and killed the saleswoman and two more women in the shop.

He then injured five other women seriously, as well as wounding a child, in a bank and on the street.

He was cornered by passers-by before the police shot him in the thigh, Kallert said.