South Korean and Japanese patrol boats are in a standoff in the East Sea over Japan's allegation that a South Korean fishing boat illegally entered its exclusive economic zone.

The standoff started at around 2 pm on Thursday in waters some 70 kilometers southeast of the Dokdo islets, South Korea's easternmost islet.

A Korea Coast Guard official says that both sides are investigating Japan's claim that the 29-ton Ssangyong intruded into the Japanese EEZ.

Four Japanese and one South Korean coast guard patrol boats are involved in the high sea confrontation.