A soft drink containing an ingredient of the impotence drug Viagra has been banned by Japanese officials.

The acted after advertisements for the drink, touted as "the solution to your night time problems", appeared in men's magazines and on the Internet.

Some 47,000 bottles of the non-prescription drink were imported from China a year ago, and all but 4,000 had already been sold, mainly in pharmacies around Nagoya, western Japan, said a local government official there.

Each bottle of the drink contained 64.3 milligrams (mg) of the chemical sildenafil, the active ingredient in Viagra, far more than the 25 or 50 mg in one tablet of Viagra sold in Japan, the official said.

"It could definitely have the same effect as Viagra," she said.

Each 20-millilitre bottle was priced at 3,000 yen (US£25), compared with 1,100 to 1,300 yen per tablet for Viagra. The official said the drink contravened Japanese drug laws.

The firm that imported the drink said it was made from squeezed Chinese fruits resembling grapes, and it was unaware of the chemical, Kyodo news agency reported.

An estimated 9.8 million men in Japan suffer from erectile dysfunction.