Shanghai Metro warned would-be "subway surfers" against copying a man who was arrested on Wednesday after he was found on top of a subway car.

Platform workers spotted the man, in his 30s, sitting on the roof of a Line 3 train at Zhongshan Park Station at about 8:30 am.

Services between Yishan Road Station and Zhongtan Road Station were suspended for nearly half an hour, stranding many commuters, especially at Zhongshan Park, a transfer station connecting Lines 2, 3 and 4.

The man has refused to cooperate with the investigation, authorities said.

"We're still verifying where he is from and how he got up there because he hasn't told us anything," police spokeswoman Zhou Wei said.

"We don't know how long he was up there before he was noticed," she said. "Chances are, he climbed up when the metro stopped at Zhongshan Park, as the speed of subway trains is about 40 km per hour, and it's impossible to climb on the train's roof when it's moving."

Police and Shanghai Metro said it is the first time they have discovered a person riding on top of a train car, and warned others not to follow suit.

"It could be life-threatening if someone climbs up to the Metro train because the high-voltage lines up there create a high risk of electric shock, and it's likely to cause serious injuries if someone falls off the roof when the train starts running," said Lan Tian of the Shanghai Metro Operation Management Center.

"Moreover, it affects the normal operation of the subway and inconveniences passengers."

Police said the man may face administrative detention of up to 10 days for disturbing public order.