North Korea has fired three ballistic missiles off its east coast, in a show of power coinciding with the G20 economic summit in China.

The South Korean military joint chiefs of staff said missiles were fired from the North Hwanghae province and landed in the Sea of Japan.

The totalitarian state regularly tests rockets and missiles, especially when international attention is turned to northeast Asia.

World leaders are gathering for the G20 summit of advanced and emerging economies in the city of Hangzhou in eastern China.

The missiles were launched just hours Chinese president, Xi Jinping, said he opposed the US deployment of an advanced anti-missile system in Korea, despite increasing international concern about the isolationist state's advances in missile technology.

Beijing is the North's only major ally, but ties between the neighbours have frayed following a series of nuclear and missile tests and other perceived acts of aggression.

South Korea's joint chiefs of staff said the three missiles, launched from the western North Korean town of Hwangju, flew across the country before landing in the waters off its east coast, but did not describe the range of the missiles.

Before the firing on Monday on the sidelines of the G20 summit, South Korean President Park Geun-hye criticised the North for what she called 'provocations' that are hurting Seoul-Beijing ties.

North Korea launch short range projectiles Show all 6 1 /6 North Korea launch short range projectiles North Korea launch short range projectiles A man watches a TV news program showing a file footage of the missile launch conducted by North Korea, at Seoul Railway Station in Seoul, South Korea, AP North Korea launch short range projectiles North Korean leader Kim Jong-un speaking during a ceremony for the scientists, technicians, workers and officials who worked on the recent successful launch of a satellite EPA North Korea launch short range projectiles People watch a TV news program showing a file footage of the missile launch conducted by North Korea, at Seoul Railway Station in Seoul, South Korea, AP North Korea launch short range projectiles North Korean soldiers guard the truce village of Panmunjom at the Demilitarized Zone (DMZ) which separates the two Koreas, in Panmunjom, North Korea AP North Korea launch short range projectiles People watch a TV news program showing North Korean leader Kim Jong Un, at Seoul Railway Station in Seoul, South Korea AP North Korea launch short range projectiles An undated file picture released by the Rodong Sinmun, the newspaper of the North Korean ruling Workers Party EPA

The launch comes four days before the 68th anniversary of the founding of North Korea's government and days after South Korean and US troops ended annual joint summertime military drills, which North Korea regularly describes as a dress rehearsal for invasion.

Last month, worries about the North's weapons programmes deepened after a missile from a North Korean submarine flew 500 kilometers (310 miles), the longest distance achieved by the North for such a weapon.

Missiles launched under water are causing concern to neighbouring countries because they are harder to detect in advance than weapons on land. The development of submarine missiles is a key step towards North Korea having nuclear capabilities.

The UN Security Council has strongly condemned four North Korean ballistic missile launches in July and August. It called them "grave violations" of a ban on all ballistic missile activity.

Successful missile tests in North Korea have previously been celebrated by mass dancing exhibitions and concerts in the country. North Korea has a "Military First" national holiday, where it rejoices in its miltary strength.