The South Korean patrol ship first found the North Korean boat shortly after 7 p.m. on Saturday and guided it to the nearby port of Mukho, Mr. Choi said.

North Korean fishing boats occasionally drift into South Korean waters after experiencing engine trouble or running out of fuel. South Korea returns those on board to the North unless they have expressed a desire to defect.

This year alone, seven North Korean boats with a total of 28 people on board have been rescued by the South Korean Navy or Coast Guard, including the boat that crossed the border on Saturday and another found off the eastern coast on June 23. Of the 28 people, 21 have chosen to return home to the North, two defected to South Korea and the five picked up on Saturday are still being questioned.

When North Koreans choose to stay in the South, the North has almost always accused South Korea of holding them against their will. South Korea, for its part, has accused the North of holding hundreds of South Korean fishermen against their will after their ships strayed into North Korean waters, or in some cases they were, according to the South, abducted by the North in the decades after the 1950-53 Korean War.

More than 30,000 North Koreans have fled to the South since a widespread famine hit their isolated and impoverished country in the late 1990s. Nearly all of them traveled through China, but some have defected through the heavily guarded land or maritime borders separating the two Koreas.