The captain of a Chinese fishing boat was arrested on Friday over allegedly operating near the inter-Korean maritime border and using an illegal drug, the Korean Coast Guard said.

Coast guard officers found methamphetamine inside the boat that they seized in waters off Socheong Island in Incheon, west of Seoul, the previous day.

On Thursday, they confiscated 0.12 gram of the drug and an inhaler from the ship's pilothouse after taking it to a coast guard station in Incheon. During an investigation into the captain, whose name was withheld, the 48-year-old man confessed that he had bought them shortly before the boat left the port of Donggang in China's Liaoning Province around 5 p.m. on June 9, they said.

The captain, who purchased the drug and the inhaler from an acquaintance for 240 yuan and 20 yuan respectively, is suspected of inhaling the stimulant three times when the boat sailed near the Northern Limit Line, the inter-Korean de facto western maritime border, this month.

He has also administered the drug about 10 times in China since last year, they said. "I used the drug in secret at the pilothouse to beat fatigue," he was quoted as saying. He tested positive in a urine test for the drug.

The Coast Guard plans to book the Chinese man without physical detention on charges of suspected violation of the illegal fishing control law concerning Korea's exclusive economic zone. In addition, it will book him on suspicion of violating the drug control law.

The Chinese fishing boat carrying five crew members traveled in waters southeast of Socheong Island south of the NLL around 6:33 p.m. on Thursday before being captured by the South Korean Coast Guard.

Illegal fishing by Chinese fishermen is a troublesome issue in the country as it has severely damaged the livelihood of Korean fishermen operating in the Yellow Sea.

Chinese fishing boats often cross into Korean waters in the Yellow Sea during peak crab season in search of bigger hauls, regularly leading to crackdowns by the Korean Coast Guard. (Yonhap)