Communist North Korea has again fired dozens of short-range ballistic missiles into the sea between the east coast of the Korean peninsula and Japan, according to South Korea's defence ministry.

Around 30 missiles were fired into the Sea of Japan early on Saturday morning (local time). Earlier in the week, North Korea fired 25 missiles from the same launch site, close to Wonsan on the country's east coast.

A spokesman for South Korea's joint chief of staff said: "North Korea fired off 30 short-range missiles between 4:00am and 6:10am this morning from its east coast into the Sea of Japan. The missiles are estimated to have flown about 60 kilometres."

This is the sixth multiple launch from North Korea in little over a month. South Korea and the west have condemned the North for what they describe as "provocative actions", but the North claim the tests are in response to the joint military drill being conducted by the US and South Korea since February.

The Key Resolve and Foal Eagle exercises take place every year but North Korea apparently believes they are rehearsals for an invasion of the totalitarian regime.

Earlier this month China expressed concern over the test firing of a rocket from North Korea, which they claim passed through the flight-path of a Chinese airliner en route from Tokyo, Japan, to Shenyang in China. The plane, carrying 220 people, passed through the trajectory of the missile seven minutes later.

A Chinese foreign ministry spokesman said then: "There were no accidents, but a very dangerous and serious situation could have occurred."

North Korea has repeatedly ignored UN resolutions calling on it to abandon ballistic technology, which is believed to have been used in the recent tests. It has also threatened to demonstrate its nuclear deterrent, possibly by staging atomic tests, as occurred in 2006, 2009 and 2013. However, Seoul does not believe another nuclear test is imminent.