The Consumer Council on Thursday urged people to use a pump to inflate balloons, rather than blowing them up by mouth, after finding a "worrying" amount on sale in Hong Kong contain excessive levels of contaminants suspected to cause cancer.

The watchdog said it recently tested 35 types of balloons and 23 of them failed European Union safety standards for the presence and release of nitrosamines and nitrosatable substances.

One type of balloon exceeded the EU limit for nitrosamines by 6.8 times, the council said.

Victor Lui, the vice-chairman of the council's research and testing committee, said people should take some precautions when handling balloons.

"To decrease the risk, I think [people should] firstly avoid using their mouths to inflate the balloon. You can use an air pump to air the balloon up," he said.

"After touching the balloon, you can use water to wash your hands and face to decrease exposure."

The watchdog said the price of a packet of balloons has no bearing on how safe the product is.

It added that it has referred its findings to Customs officials.