The anti-impotence drug Viagra has made its debut in China following successful trials of the drug on hundreds of men across the country.

A hospital in the southern city of Shenzhen, close to Hong Kong, is reported to have written the first prescriptions for six patients, including a 70-year-old man.

According to some reports, tens of millions of Chinese men suffer from some form of sexual dysfunction.

However, the company behind the pill, US drug giant Pfizer, says it does not yet know exactly how big their market will be.

It says sales will depend in part on improving the ability of Chinese doctors to diagnose sexual problems and on more Chinese men overcoming their embarrassment.

"If we are successful, it means that we are reaching patients who are currently suffering in silence," said Koenraad Bosteon, chairman of Pfizer's Chinese arm.

Fake viagra

The introduction of Viagra has aroused widespread curiosity in China, a country that has a long-standing preoccupation with drugs designed to increase sexual potency.

During local trials of Viagra, correspondents say many Chinese drug producers rushed to capitalise on the publicity, selling fake versions, or their own drugs under similar names.

In April, one company was ordered to withdraw pills marketed as "Weige" - meaning "Great Man" - because of its resemblance to Viagra.

Nicknamed "Big Brother Wei", the pill has been available on the black market for almost two years since it was first introduced in the United States.

Correspondents say that, for many Chinese men it is not just an interest in sex but the belief that intercourse helps to prolong life, which has for centuries led them to try a variety of sexual tonics.

Among the more traditional remedies for impotence have been potions made of Chinese herbs, tiger bones, deer antlers and even seal penises.