SEOUL: North Korea is building a new hovercraft base that would allow it to launch a quick invasion of South Korean islands near the disputed Yellow Sea border, media reports said Tuesday.

The base is under construction just 50-60 kilometres (30-35 miles) from Baengnyeong, the closest South Korean island to the North Korean coast, three major newspapers cited military or government sources as saying.

The defence ministry declined to confirm the reports, which came just over two months after the North shelled one of the border islands.

A government source told Chosun Ilbo that South Korean and US intelligence late last year detected construction for the base at Koampo in Hwanghae province.

It could apparently accommodate up to 70 hovercrafts which could each carry a platoon of commandos and travel up to 90 kilometres per hour across the sea and tidal mudflats, the daily said.

Once the base is completed, North Korean troops would be able to land on the South's strategically important frontier islands in 30 to 40 minutes, it said.

JoongAng Ilbo said the North already has a hovercraft base at Cholsan near the border with China.

"The new base in Koampo represents the forward deployment of North Korean hovercraft capable of infiltrating commandos into South Korea," a military source was quoted as saying.

Cross-border tensions have been acute since a South Korean warship sank last March near the Yellow Sea border after what the South said was a torpedo attack, a charge denied by Pyongyang. The sinking cost 46 lives.