A 17-year-old Afghan refugee was shot dead by police after injuring four passengers in a slashing attack aboard a train late yesterday near Wuerzburg in the southern German state of Bavaria, authorities said.

Three of the victims were critically wounded.

An initial investigation found that the attacker, who wielded a knife and an axe, came to Germany as an unaccompanied minor, Bavarian Interior Minister Joachim Herrmann told German broadcasters.

Asked if the violence was fuelled by Islamist motivations, Herrmann said the suspect had shouted something in connection with the attack, but that the investigation was still under way.

The commuter train was travelling from Treuchtlingen to Wuerzburg at the time of the attack.

In addition to the wounded, 14 people aboard the train were receiving care for shock.

After the attack, the boy tried to flee. A police special operations unit, which happened to be nearby at the time of the incident, pursued the suspect, who was shot dead when he tried to attack the officers.

Based on witness accounts, police believe the boy acted alone, Herrmann said.

The boy, who arrived in Germany without his parents, had lived in a refugee home in Ochsenfurt in the Wuerzburg area, and most recently was with a foster family.

German media, citing a spokesperson for the Bavarian interior ministry, reported that the man had shouted "Allahu Akbar" (God is great) during the attack, but neither Herrmann nor Hench said they could confirm that.

"There are witnesses that suggest there may be an Islamic background to this but that is far from clear at this point," Herrmann said.

Unlike neighbours France and Belgium, Germany has not been the victim of a major attack by Islamic militants in recent years, although security officials say they have thwarted a large number of plots.

Germany welcomed roughly 1 million migrants in 2015, including thousands of unaccompanied minors. Many were fleeing war in countries like Syria, Iraq and Afghanistan.

- Agencies