South Korea's top court on Friday confirmed the prison sentences of two Chinese skippers convicted of illegally fishing in South Korean waters and injuring local Coast Guard officials in a violent clash about a year ago.

The Supreme Court delivered sentences of up to three and a half years to the two and ordered the confiscation of their two boats.

It also confirmed the sentences handed down to two of their subordinates, who had been given sentences of two years and one and a half years, after a two-year suspension.

The four were convicted of causing bodily harm to South Korean officials, who were trying to rein them in from fishing in local waters in the Yellow Sea off the coast of Gunsan, about 270 kilometers south of Seoul, in December 2013.

They were also found guilty of fishing 1,000 kilograms of pollack in local waters.

The four had filed for an appeal to overturn the seizure of the boats.

The Supreme Court, however, said the penalty was fair, as the lower courts "did not misconstrue the legal principles for confiscation."

Chinese fishing boats often cross into South Korean waters in the Yellow Sea in search of abundant fish stock, regularly leading to violent clashes between Chinese crews and the South Korean Coast Guard.

In 2011, a South Korean Coast Guard officer was killed by Chinese fishermen in one such instance.

The Coast Guard said it arrested 183 Chinese fishermen in 2013 over illegal fishing in the Yellow Sea. (Yonhap)