A total of 80 Vietnamese fishermen and nine Vietnamese fishing ships suspected of illegally entering Chinese waters were detained in South China's Hainan Province, the Hainan Daily newspaper reported Monday.

Meanwhile, frontier public security forces in Hainan have also expelled 38 Vietnamese fishing ships suspected of the same activities, the report said.

Nine detained ships did not have valid certificates for sea operations required by relevant Sino-Vietnamese agreements.

Chinese authorities said they illegally went beyond the boundary and entered the Beibu Gulf fishing area, the report said, adding that the behaviour had violated agreements signed by China and Viet Nam.

The Vietnamese detainees all confessed to doing so and the case is under further investigation, the report said.

It added that the Vietnamese fishermen are safe and their accommodation is ensured by frontier public security forces at the Basuo Port in Dongfang, a city in Hainan.