Guangzhou Metro has introduced women-only carriages during rush hours as it looks to stamp out sexual harassment.

The city's subway system, which turns 20 this year, began piloting the service on Line 1 on Wednesday, with each train having one "ladies-first" car.

Guangzhou Metro Corp, the network operator, said male passengers are not prohibited but are encouraged to avoid the cars during morning and evening rush hours.

The company is alerting passengers to the service through posters and ground stickers on platforms and in carriages. Volunteers are also spreading the word at stations.

"We hope to promote the civilized concept of caring and respecting women through long-term advocacy," the company said in a statement.

The service was first proposed by Su Zhongyang, a member of the Guangdong provincial committee of the Chinese People's Political Consultative Conference, as a way to prevent sexual harassment on crowded trains.

Guangzhou Metro has 10 lines and carries 7.3 million passengers a day on average.