Nearly 1,000 foreign minors were found living in the city illegally last year, up from 2009, the Shanghai Exit-Entry Administration Bureau said yesterday.

The figure accounted for about 20 percent of all foreigners living illegally in Shanghai last year. Among the minors caught staying illegally, nearly 70 percent were of Chinese descent. The bureau declined to reveal more detailed statistics.

According to the bureau, many of these cases occur because visas are not extended by parents or grandparents.

The bureau said many of the children have Chinese parents but hold foreign passports. Their parents send the child back to China to be taken care of by grandparents. Often the grandparents don't know about visas and fail to apply for extensions.

Last month, twin brothers who were born in the United States were stopped at a Shanghai airport when they were planning to return to the United States. They had lived with their grandmother in Shanghai for more than a year. The grandmother failed to extend their visas, which had expired eight months ago.

Li Feng, an official with the bureau, said the validation for such visas is usually six months, and one can apply for a six-month extension.

The bureau also said some parents are too busy and forget to take care of their child's visa.

If foreign minors are caught living illegally in Shanghai, their parents or guardians will be fined. In serious cases, a permanent record could be left, which is likely to affect future visa applications.

The bureau reminded foreigners to keep visas up to date for all family members.