SEOUL: North Korea fired three ballistic missiles off its east coast Monday, Seoul said, a new show of force that comes as top world leaders meet at the G20 summit in China.

The missiles were fired into the Sea of Japan (East Sea) from the North's Hwangju county at around 0300 GMT, a defence ministry spokesman said, more sabre-rattling that follows a submarine-launched ballistic missile test some two weeks ago.

“They are speculated to be Rodong missiles with a range of 1,000 kilometres and were fired without navigational warning to Japan,” the spokesman said in a statement.

“North Korea's ballistic missile launch is a direct violation of UN Security Council resolutions aimed at showing off its nuclear and missile capabilities during the G20 summit,” he added.

Japan's defence ministry said that the three missiles are estimated to have fallen into the country's Exclusive Economic Zone (EEZ) in the Sea of Japan, according to a statement.

“The ministry expresses serious concern over the missile launches as they pose a grave threat to Japan's national security,” a ministry statement said.

Monday's missile launch came hours after South Korean President Park Geun-Hye and Chinese President Xi Jinping met on the sidelines of the G20 Summit in Hangzhou.

Ties between South Korea and China have been frosty since Seoul announced its plan to deploy a US anti-missile system in July to counter growing nuclear and missile threats from the North.

During the summit, Xi reiterated Beijing's opposition to Seoul's planned deployment of the Terminal High Altitude Area Defence (THAAD) system, arguing that “mishandling” the issue could “intensify disputes” in the region, China's state-run Xinhua news agency said.

Park labelled North Korea's continued provocations as a “challenge” to Seoul-Beijing ties, adding that security threats from Pyongyang were at an “unprecedented level”, South Korea's Yonhap news agency said.

North Korea has conducted a series of missile tests this year in defiance of UN sanctions imposed after its fourth nuclear test in January. The most recent was a submarine-launched ballistic missile last month.

The missile, fired from off the northeastern port of Sinpo, flew 500 kilometres towards Japan, far exceeding the range of the North's previous sub-launched missiles.

North Korean leader Kim Jong-Un described the August test as the “greatest success” and said it put the US mainland within striking range.

The launch was widely-condemned by the US and other major powers and marked what weapons analysts said was a clear step forward for North Korea's nuclear strike ambitions.

A proven submarine-launched ballistic missile system would allow deployment far beyond the Korean peninsula and a “second-strike” capability in the event of an attack on the North's military bases.