Police have detained a man for unhooking a fellow passenger's bra at the Pudian Road Station on metro Line 6, local media reported Wednesday.

The man was one of 19 suspects whom metro police have detained for harassing women since they launched a campaign against sexual harassment in June, according to a press release from the Shanghai metro police. Police said they see more sexual harassment cases in the summer due to the hot weather.

Sexual harassment includes behavior such as groping and taking photos up women's skirts. To fight the problem, metro police have assigned more officers to stations where sexual harassment occurs more frequently, especially during rush hours, the press release said.

On July 3, police detained a 25-year-old suspect surnamed Sun for allegedly touching a woman's waist around 8:40 am at Lujiazui Station on metro Line 2.

Officers pay special attention to men who closely follow female passengers, according to the press release.

On July 20, police detained a suspect surnamed Zong for reportedly taking photographs up a woman's skirt around 8:35 am at the Jinjiang Park Station on metro Line 1.

Anyone caught harassing women can be detained for five to 10 days, said Zhou Wei, a press officer with the metro police.

Sexual harassment often goes unpunished on the subway because many women are unwilling to call the police, making it difficult for them to collect evidence, Zhou told the Global Times.

Last month, a passenger photographed a man who repeatedly groped a female passenger on the subway. The woman did not protest or call for help. Her only response was to move her handbag between herself and the other passenger.

The man continued to touch her legs and followed her even after she stood up and moved to the train doors.

Although police had photos of the man, they were unable to pursue the matter because the victim was unwilling to come forward.

Some victims remain silent because it is difficult to prove that another passenger sexually harassed them, said Zhang Zhenyu, a psychologist with the Shanghai Psychological Society. Some feel embarrassed to tell others that they had been targeted.

Police have been urging women to shout for help if they are sexually harassed on the subway. They also encourage other passengers to lend a hand in such cases.