South Korea has deployed "dozens" of short-range missiles a few kilometres off the North Korean coast, a day after three missiles were fired from the Communist state.

The Israeli-made missiles have been stationed on the Yellow Sea islands, around 11 km from the North Korean border.

A senior South Korean military official told the country's Yonhap on condition of anonymity: "Dozens of Spike missiles and their launchers have recently been deployed on Baengnyeong and Yeonpyeong islands. They can destroy [North Korea's] underground facilities and can pursue and strike moving targets."

The satellite-operated missiles have a strike range of about 20km.

The latest development is in response to North Korea's deployment of multiple rocket launchers in the border region. South Korean officials believe North Korea has also deployed 76.2mm coastal guns which have a strike range of about 12km.

A state-run South Korean thinktank had earlier estimated that North Korea may possess around 200 missile launchers, almost double the figure previously estimated.

North Korea is believed to have used a multiple rocket launcher in its latest launch of missiles.

"The missiles travelled about 120㎞, and in the North Korean arsenal, only the modified KN-02 or multiple rocket launchers of 300㎜ or larger in calibre can go that far. It's possible that North Korea fired both KN-02 missiles and its multiple rocket launchers," the source told Yonhap.

North Korea has not officially commented on its missile launch, which South Korea's presidential office said was not a serious security threat.

Some experts believe North Korea's launch was part of a military exercise while others suggest it was a deliberate attempt to provoke the US and South Korea.