One person was killed and several were injured in an attack by a lone knifeman in a supermarket in the northern German city of Hamburg on Friday, police said.

The police said the man had suddenly started attacking customers in the shop before fleeing, pursued by witnesses. Officers detained him near the site.

There was no immediate indication of any political or religious motive for the attack.

"We have no clear information as to the motive or the number of wounded," Hamburg police said in a tweet. "It was definitely a lone attacker."

Police have been on high alert in Germany since a spate of attacks on civilians last year, including a December attack on a Berlin Christmas market, when a hijacked truck ploughed into the crowds, killing 12 and injuring many more.

Security has been a campaign issue ahead of Sept. 24 parliamentary elections, in which Chancellor Angela Merkel is expected to win a fourth term in office.

Newspaper Bild showed a picture of the alleged Hamburg attacker sitting in the back of a police car, his face concealed with a bloodied shroud.

A video on its website showed a helicopter landed outside the supermarket with armed police in body armour patrolling the neighbourhood.