A spokesman for Shenzhen's Family Planning Bureau said the number of condom machines in the city would be increased from 30 to up to around 800 by the end of the year.

The machines were introduced earlier this month because an increase in the number of people living in tower blocks meant it was no longer possible to deliver contraceptives door-to-door.

Wang Zhiqiang, an official of the city's Family Planning Bureau, said there was also a concern at the prevalence of sex outside marriage in the city, particularly among its estimated three million migrant workers.

He said the introduction of the machines would help prevent the spread of sexually- transmitted diseases as well as pregnancies unapproved by the authorities.

Mr Wang said the condoms, sold at subsidized prices, were better quality than the often shoddy goods available in local shops.

He said the first batch of machines had been so popular that 20 more had been installed, offering not just local but imported products as well as contraceptive pills - and more were planned.

China, which is facing a fast-growing HIV problem, recently announced a plan to make it easier to buy contraceptives.