An off-duty Swedish police officer has been hailed after catching a brazen thief while out catching some rays.

Mikaela Kellner was sunbathing in a Stockholm park with a friend when she realised a cunning pickpocket had walked off with her pal's mobile phone.

Despite wearing only a bikini, the athletic officer chased after him and pinned him to the ground, with the remarkable arrest being caught on camera.

"I would have stepped in no matter my outfit," she told Sweden's English-language news site The Local as she recounted her act of heroism.

Ms Kellner said the man had approached them pretending to sell magazines for the homeless and remained loitering around their blankets.

"I told my friends to keep an eye on their things. But as soon as he left one of my friends said 'where did my mobile phone go?'" she explained.

Ms Kellner said she "just acted on instinct" as she overpowered the man and wrestled him onto the grass with the help of a fellow officer.

"There was no time, so I ran after him, maybe 15 metres or so," she said. "One of my friends is also a police officer, so we got hold of him. He tried to get away so we held onto him harder."

Ms Kellner, who has served in the police force for more than a decade, said she had received a "lot of positive comments" from friends and colleagues after posting the image on her Instagram page.

She said it was only after she had the thief pinned down that she realised the arrest would have appeared a little less than routine to her fellow parkgoers.

"When I sat there I looked over at our other two friends who are not police officers and realised that it probably looked pretty funny," she said.