HONG KONG, Sept. 21 -- A total of 18 illegal workers and five suspected employers have been arrested in a series of enforcement operations this week, the Immigration Department (ImmD) of China's Hong Kong Special Administrative Region government announced Thursday.

In an operation codenamed "Twilight," the ImmD Task Force officers raided 21 target locations including restaurants, a beauty center, retail shops, a garbage collection depot, a residential building and an industrial building. Seven illegal workers and four employers were arrested.

In a joint operation with the Hong Kong Police Force codenamed "Champion," enforcement officers raided 27 target locations in Tuen Mun in the New Territories, including a food processing factory, warehouses and industrial buildings. Seven illegal workers and an employer were arrested.

In another joint operation "Windsand," four visitors were arrested for breaching their conditions of stay by being involved in suspected parallel goods trading.

"Any person who contravenes a condition of stay in force in respect of him shall be guilty of an offence. Also, visitors are not allowed to take employment in Hong Kong, whether paid or unpaid, without the permission of the Director of Immigration," an ImmD spokesman said.

"Offenders are liable to prosecution and upon conviction face a maximum fine of 50,000 Hong Kong dollars (about 6,374 U.S. dollars) and up to two years' imprisonment. Aiders and abettors are also liable to prosecution and penalties," the spokesman added.