SEOUL: Residents of a South Korean island closest to the tense sea border with North Korea have shrugged off a warning from Pyongyang urging them to flee ahead of "thunderous attacks", an official said Sunday.

The North's official website, Uriminzokkiri, told residents of five islands south of the border to leave, warning of "devastating consequences" if recent cross-border tension escalates into a full-scale conflict.

"The wisest choice when the fire of thunder rains down on you is running afar," it said in an editorial published late Friday.

It repeated criticism of an ongoing South Korea-US joint military drill, calling it a rehearsal for war that may prompt counter-attacks from the North.

"At a time like this... it will be the best for the residents at the five border islands like Baengnyeong and Yeonpyeong, the biggest flashpoint area between two Koreas... to evacuate as soon as possible," it said.

A North Korean artillery attack on Yeonpyeong island, in the Yellow Sea, in 2010 killed four South Koreans.

Young North Korean leader Kim Jong-Un recently threatened to "wipe out" the neighbouring island of Baengnyeong.

The latest threat however had caused little panic among the 5,000 residents of Baengnyeong, the closest island to the border, said an administrative official on the island.

"There's no visible sign of panic or mass exodus... people appeared to be accustomed to it to some degree," the official, who declined to be named, told AFP by telephone.

"They are less worried about the situation than people outside believe," she said, adding the authorities however had stocked up underground shelters and been holding daily drills to prepare in the event of a bombardment.

The disputed maritime border in the Yellow Sea has seen bloody naval clashes in the past and, with military tensions at their highest levels for years, is seen as the prime location for another confrontation.