Many passengers were not buying tickets when taking the Metro, the Daily Sunshine reported.

The newspaper said that a common practice is for two people to enter through a gate after one has inserted his ticket into the machine, taking advantage of the time gap before the gate closes.

Most cases happened at machines when Metro staff members were not watching.

Some passengers said they had seen cases like this occur many times, especially at crowded stations.

The station authority said it had too many areas to monitor. "There are loopholes that can be exploited when our attention was shifted to other places," the center said.

A Metro employee said she witnessed at least 20 ticketless travelers each day at the station where she worked, which saw daily passenger traffic between 20,000 and 30,000. According to her, busy stations such as Luohu Station and Dongmen's Laojie Station, which handle between 50,000 and 60,000 people each day, suffer the most.

The Metro rules state that defaulters will be fined between 15 yuan (US$1.85) and 50 yuan.

The Metro said it lost a lot of money due to ticketless travelers.

According to an engineer with the company which designed the Metro's automatic ticket-checking system, the gate was designed to remain open when encountering an obstacle. "We make it that way to avoid injuries," he said.

He said usually the gate will remain open for a few seconds after one person walks through. A red light will blink if someone passes through without a ticket, but that could be easily ignored if there were no staff watching.

Editor: Donald