A man armed with a knife stabbed five people on Thursday inside the centre south of the Italian city of Milan, killing one person.

Police arrested a 46-year-old Italian man suspected in the attack at a shopping centre in Assago, a suburb of Milan.

A supermarket employee died en route to the hospital, according to the news agency ANSA, which said three other victims were in a serious condition.

Another person was treated for shock but not hospitalised, police said.

The motive for the attacks was unknown, but police said the man showed signs of being psychologically unstable. There were no elements to suggest terrorism.

Spanish player Mari, who is on loan from Arsenal at the Italian Serie A club Monza, was among the wounded.

"Pablo Mari had a fairly deep wound on his back, which fortunately did not touch his vital organs such as the lungs or others," Monza CEO Adriano Galliano told Sky Italy.

"His life is not in danger, he should recover quickly. We hope to see him back soon."

Arsenal manager Mikel Arteta says Mari "seems to be OK" and confirmed the defender is in hospital.

"I know (club technical director) Edu has been in touch with his relatives," said Arteta after Thursday's 2-0 defeat at PSV Eindhoven in the Europa League.

"He is in hospital. He seems to be okay. I will get a briefing now about what happened."

Arsenal issued a club statement, saying: "We are all shocked to hear the dreadful news about the stabbing in Italy, which has put a number of people in hospital including our on-loan centre-back Pablo Mari.

"We have been in contact with Pablo's agent who has told us he's in hospital and is not seriously hurt.

"Our thoughts are with Pablo and the other victims of this dreadful incident."

Australian Associated Press