Image copyright AFP/JIJI Image caption Mayu Tomita received nearly two dozen wounds to her neck and chest

A Japanese pop star is in a critical condition after being repeatedly stabbed by a fan as she was waiting to perform at a concert venue in Tokyo.

Mayu Tomita, 20, received nearly two dozen wounds to her neck and chest.

Police arrested Tomohiro Iwazaki, 27, at the scene. He is reported to have said he was angry because Ms Tomita returned a gift he had sent her.

The singer had reportedly complained to police about the fan last month.

Japanese media says she contacted police after Mr Iwazaki started posting obsessive comments about her on Twitter and other social media sites.

When police arrested him after the attack, he is reported to have told them that he ambushed her at the station and asked her about the gift.

"I lost my temper because she didn't clearly answer," he reportedly said.

Ms Tomita had been working as a pop star and actor while completing her college studies.

In 2014, two teenage members of Japanese girl group AKB48 were attacked by a man wielding a saw at one of the band's regular meet-the-fans events.