German police shot dead a 17-year-old Afghan refugee Monday after he attacked train passengers with an axe and a knife, seriously wounding four in what one official said was a "probable" extremist attack.

German police shot dead a 17-year-old Afghan refugee Monday after he attacked train passengers with an axe and a knife, seriously wounding four in what one official said was a "probable" extremist attack.

Several other people were also injured in the assault on a regional train near the southern city of Wuerzburg, police said, adding that the teenager was killed as he tried to flee.

Joachim Herrmann, the interior minister of Bavaria state, said the assailant had arrived as an unaccompanied minor in Germany and had lived at first in a shelter and then more recently with a foster family in nearby Ochsenfurt.

"It is quite probable that this was an Islamist attack," said a ministry spokesman, adding that the assailant had shouted "Allahu akbar" (God is greatest).

However he stressed that the investigation was ongoing and that the teenager appeared to have acted alone.

The attack happened around 9:15 pm (1915 GMT) on the train, which runs between Treuchlingen and Wuerzburg in Bavaria.

Four people were reported seriously injured and one other lightly injured. Fourteen people were treated for shock.

An eyewitness who lives next to the railway station told DPA news agency that the train, which had been carrying around 25 people, looked "like a slaughterhouse" after the attack, with blood covering the floor.

The man, who declined to give his name, said he saw people crawl from the carriage and ask for a first-aid kit as other victims lay on the floor inside.  

"The perpetrator was able to leave the train, police left in pursuit and as part of this pursuit, they shot the attacker and killed him," a police spokesman said.

Hermann later said that the teenager was shot when he attacked police while trying to escape the scene.

A special police force unit happened to be nearby and was able to mobilize quickly, Hermann added.

Germany has thus far escaped the kind of large-scale Takfiri attacks seen in the southern French city of Nice last week, in which 31-year-old Mohamed Lahouaiej Bouhlel used a truck to mow down people leaving a Bastille Day fireworks display, killing 84 people. The attack was claimed by the Takfiri ISIL group.

In May in Germany, a mentally unstable 27-year-old man carried out a knife attack on a regional train in the south, killing one person and injuring three others.