Take a deep breath, sneak under the ticket turnstile and scurry away ― that is what they do to steal a ride on Shanghai's metro.

Twenty-one people were recorded involved in such freeloading in a recent popular 96-second video filmed at a ticket gate of the city's Longyang Station on lines 2 and 7.

The harshest punishment, according to the metro authority, is a fine of 55 yuan ($8.90).

Lan Tian, spokesman for Shanghai Metro's operation management center, told China Daily that during rush hour more than 50 inspectors check the city's metro stations to ensure commuters pay for their rides.

"Of course, not all the 288 stations are covered as we're short of people," Lan said.

He said metro staff also get help from the police and security guards if they need to check people's ID.

Bao Chenglin, deputy director of the Xujiahui station of the Shanghai urban rail and bus police, said each metro station has one police officer in case a "dispute occurs between ticket evaders and metro staff".

The maximum fine, according to Lan, should be less than five times the most expensive metro fare in Shanghai, which is 11 yuan.

"But we usually ask them to buy a replacement ticket rather than ask for the 55 yuan fine," he said.

Lan said big metro stations such as Xujiahui, People's Square and Zhongshan Park see more freeloaders, as these stations see more types of commuters. And fare evasion usually spikes before holidays such as Spring Festival, which falls on Feb 10 this year.

Garbage collector Xing Chen from Hunan province visits four to five Shanghai metro stations every day without buying any tickets.

"I sneak in and out to collect plastic bottles," said Xing, adding that he's only doing that inside metro stations in the winter because it's cold outside.

"They put more manpower to catch freeloaders in some of the big stations such as the Shanghai Railway Station. I was caught a few times, but nobody fined me, they just asked me to buy the ticket."

The city's local newspaper Shanghai Morning Post said that people riding for free are ripping off the metro system about 10 million yuan a year. An estimated 0.16 percent of the city's daily 6 million metro riders never pay for their tickets.

But the percentage of freeloaders in Shanghai's big metro stations reaches 2 to 3 percent, said the newspaper.

"It's hard to estimate the percentage of riders taking free rides because it varies from station to station and from time to time," said Lan, without offering a figure.

The person who recorded the popular short video, who identified himself only as Chen, said more than 1 million people watched his footage since he uploaded it to youku.com on Monday.

"And 21 ticket evaders in 96 seconds is not the highest. I saw more than 30 people do it within one minute during the evening peak period," said Chen.

The video recording, which shows that most of the freeloaders seem to be migrant laborers, also triggered heated discussion about whether migrant laborers are more likely to be ticket evaders.

However, Wu Yizhong, a 28-year-old white-collar worker from Shanghai, said she rode the metro free when she lost her ticket once. "I saw many people do it, including white-collar workers and local students who were speaking Shanghainese. I don't think it's only migrant workers," she said.