People from northern China are using forged South Korean passports to fly to Hong Kong and illegally migrate abroad, the Immigration Department says.
A spokesman said a large rise in the use of South Korean travel documents, mostly photo-substituted, was detected in the past 16 months.
Ethnic Chinese from Heilongjiang province were using them in an attempt to fly to Canada and Europe.
Immigration officers were detecting an increasing number of doctored passports.
The original holder's photograph was usually removed and replaced with that of the illegal immigrant.
Many Koreans lived in northern China and often tried to use South Korean passports to take Chinese wives or relatives to live abroad, the spokesman said.
Immigration records showed 13 forged South Korean passports had been found in the first four months of this year and 65 last year.