Two men travel in a subway coach without pants to campaign for a better environment in Guangzhou, Guangdong province, on the "no pants day" on Sunday. [Meng Zhubin/China Daily]

In response to a group of young people who rode the subway without trousers in three days ago, metro operators said the event "posed threats to riding safety and social order".

Between the Wangshengwei and Sun Yat-sen Memorial Hall stations of Guangzhou's metro line 2, some 20 young people rode without trousers on Sunday, with environmental slogans and words written on banners and on their underwear or shorts.

Liang Shuxin, the organizer of the event, said it was aimed at promoting a low carbon lifestyle and an environmentally friendly Asian Games, which will open in the city in November this year.

"We did not notice the event on that day since they slipped off their trousers after they entered the coaches," Ye said.

"Their behavior angered not only us, but many parents who have complained to us," Ye told China Daily yesterday.

The company will take every measure possible to stop such unusual events from happening in the future, Ye said.

"Any event should be conducted in accordance with regulations and should be accepted under social ethics. Riding without trousers in public areas such as subways is not acceptable by the majority of people," Ye said.

Sources with the company said anyone riding in the subway without pants would be punished in accordance with civil regulations.

The event on Sunday was one of the many that has already taken place in some 44 cities across 16 countries and regions. It was believed to be the first of its kind across Chinese cities.

"It will bring about negative impacts to some people, specially senior citizens and parents. They hardly know relations between no-pants riding and environmental protection," said Cao Yixin, a student with Sun Yat-sen University.

Participants should take Chinese culture into consideration when they take part in such events, Cao said.

"Many Chinese people, even us college students, can hardly accept such a move in public areas," she told China Daily.

Huang Huiju, a mother with a 7-year-old daughter, said the move had nothing to do with environmental protection.

"I don't see any relation between such a move and a lower-carbon lifestyle. Trousers are necessities we need every day," she said.

Huang and her daughter were among hundreds of passengers to witness the campaign on Sunday.

"I covered up my daughter's eyes. A young man quickly took off his trousers after he entered the coach. It made me very embarrassed," she said.

Wang Yao contributed to the story