North Korea has completed a hovercraft base which could be used to attack South Korean islands near the disputed Yellow Sea border, a report said Thursday.

Recent satellite photos showed construction had finished at the base at Koampo, 50-60 kilometres (30-35 miles) from the nearest South Korean island, Yonhap news agency reported.

It cited an unidentified senior Seoul official. The defence ministry was not immediately available for comment.

"The sea at Koampo is currently frozen... but the military is closely watching it because hovercraft may be deployed there once the weather warms up," Yonhap quoted the official as saying.

It said the base can accommodate up to 70 hovercraft, which can travel up to 96 kilometres an hour across the sea and tidal mudflats and carry artillery as well as troops.

The South's military command in charge of the maritime border is devising strategies against potential hovercraft-borne attacks, said the official quoted by Yonhap.

The border off the west coast was the scene of deadly naval clashes in 1999, 2002 and 2009. In November 2010 the North shelled a frontier island and killed four South Koreans including two civilians.

Seoul since then has strengthened troops and weaponry on its five "frontline" islands.

Pyongyang refuses to recognise the boundary drawn by United Nations forces after the 1950-53 war and insists it should be moved southwards.