Every year, many women travel from the Chinese mainland to Hong Kong to get vaccinated against human papillomavirus, or HPV, a major cause of cervical cancer.

Jessica Cai, of Taizhou in Jiangsu province, has traveled to the city three times in the past six months to get inoculated, as the vaccine is not available on the mainland.

"The medical service in Hong Kong is safe and well-developed," said the 27-year-old, adding that her confidence in the city's hospitals is another reason she goes there for treatment.

Ong Yeu-theng, a gynecologist at a women's clinic in Central district, said she has noticed a rise in mainland clients seeking HPV vaccines in recent years.

She said awareness of this sexually transmitted disease has spread through word-of-mouth and that her clients have referred friends and relatives to her clinic for vaccinations.

A course of HPV inoculations at a private clinic costs about HK$4,500 ($580), according to the Cancer Fund, the largest cancer support organization in Hong Kong.

Patients receive three doses of the vaccine over six months, which means people like Cai need to pay for flights to the city and accommodation. The vaccine alone cost Cai almost HK$2,400.

Li, a hospital doctor in Heilongjiang province who did not want to be identified, said any HPV vaccine must undertake a series of clinical trials on the mainland before it can receive approval to enter the market.

Three types of vaccine are now marketed in Hong Kong: Cervarix, Gardasil and Gardasil 9, which protect against up to nine strains of the HPV.

In Hong Kong, cervical cancer was the seventh most common cancer among women in 2013, with 503 new cases and 142 deaths, according to the city health authority.

According to research led by Chen Wanqing of Beijing's National Cancer Center, the mainland had an estimated 100,000 new cases of cervical cancer last year.

Li Yinze contributed to this story.