Police on the mainland have detained eight men suspected of being involved in a major kidnapping case in Hong Kong.

Ransom of HK$2.83 million ($365,200) and stolen watches, jewelry and other valuables were seized in an operation involving officers from the mainland and the city, said Guo Shaobo, deputy director-general of Guangdong province's Department of Public Security.

The arrests came after a suspect surnamed Zheng was detained by Hong Kong police at the Luohu checkpoint on May 3 as he tried to enter Shenzhen in the province.