SHANGHAI - There have been a number of complaints during the past few days about staff members smoking on the Beijing-Shanghai high-speed trains.

Sun Honggang, a researcher from the Center for the Study of Contemporary China at Tsinghua University, wrote on his Sina Weibo, the Chinese version of Twitter, that four members of the train's staff were found smoking on the high-speed train he was taking from Shanghai to Beijing on the night of Aug 7.

When the train was about to approach its destination, passengers in the rear part of the third carriage started to quarrel with a group of train attendants and railway policemen who were smoking in a vacant sightseeing carriage.

The quarrel lasted for about 40 minutes till the train arrived at Beijing, when only one of the smokers, a 57-year-old railway policeman, apologized to the passengers.

"The policeman explained that one staff member's relatives had just passed away and they were smoking to ease his sadness," Sun said on his Weibo.

"At first I was not going to publicize this on Weibo, because it might mean the staff are laid off. But it is a security issue," Sun said.

A man working for a Beijing-based media company, who asked for anonymity, was on board the same carriage. He told China Daily that the railway policeman and several train attendants were smoking on the train, but added that some of the train staff made sincere apologies to the passengers.

"The conductor apologized especially politely. She followed us to the exit and apologized all the way," he said.

"I am most worried about the conductor now and she wasn't one of the ones smoking," he added.

The incident is not the first of its kind.

The G140 train heading from Shanghai to Beijing was 40 minutes later than scheduled on Aug 6 because of bad weather. A train attendant smoked at the door of the carriage when the train stopped temporarily at Tianjin South Railway Station.

"The train attendant apologized immediately to the passengers and explained that he had been working continuously for 23 hours," said a netizen called Lucky Fengfeng on his Sina Weibo.

Hu Jinghong, director of the news department of the Shanghai Railway Bureau, said she had found out about the incidents on the Internet and had not yet heard whether the train attendants involved had been punished.

The smoking incidents have led to some questioning whether there are smoke alarms on the high-speed trains, and, if so, whether they work or not.

"I have heard that smoke alarms are installed in some parts of the train. I am not sure whether the sightseeing carriages have alarms or not," said Hu.

Smoking is banned on the high-speed train and reminders are regularly broadcast on every train. According to the railway fire safety regulations released by the Ministry of Railways in 2010, it is the train attendants' responsibility to stop passengers from smoking on the trains.

A Beijing-Shanghai high-speed train was forced to slow down when it approached Shandong's Dezhou city on July 5 when a passenger was discovered smoking on the train. He was fined 50 yuan ($7.80) for violating the regulation.