North Korea has fired three ballistic missiles off its east coast, according to South Korea's military, in a show of force apparently timed to coincide with the ongoing G20 economic summit in China.

South Korea's joint chiefs of staff said in a statement on Monday that the three missiles, launched from the western North Korean town of Hwangju, flew across the country before splashing in the Sea of Japan off its east coast.

All three missiles were medium-range Rodong class and flew about 1,000km, South Korea's military said.

At least one of the missiles fell into Japan's Air Defence Identification Zone, a South Korean military official told Reuters news agency by telephone.

The development came as world leaders gathered for the G20 summit of advanced and emerging economies in Hangzhou in eastern China.

It also came four days before the 68th anniversary of the founding of North Korea's government, and just days after South Korean and US troops ended annual joint military drills.

South Koreans protest against missile defence shield deployment

Earlier on Monday, speaking in Hangzhou, South Korean President Park Geun-hye criticised the North for what she called provocations that were hurting South Korea-China ties.

Shortly after the missile launches, she and Shinzo Abe, Japan's prime minister, met and agreed to cooperate on monitoring the situation, according to a Japanese statement.

Al Jazeera's Adrian Brown, reporting from Hangzhou, said: "This latest [missile] incident came as China expressed unhappiness over Seoul's threats to deploy a defence shield in response to Pyongyang's continued attempts to refine and perfect its nuclear missile programme.

"China regards this missile-defence shield as a threat to its sovereignty. But we have got a reminder this morning of why South Korea feels so vulnerable."

The European Union issued a statement following the launches, calling on North Korea to end "illegal actions", which were "yet another in a string of serious violations" of the country's international obligations as set out in UN Security Council resolutions.

North Korea "must halt all missile launches using ballistic missile technology and abandon its ballistic missile programmes in a complete, verifiable and irreversible manner," the EU said in the statement.

Such launches "serve no purpose other than increase tensions to the detriment of all", it added.

Regular missile tests

North Korea regularly engages in missile and rocket tests, especially when international attention is turned to Northeast Asia.

It has staged several missile tests this year, the most recent being a submarine-launched ballistic missile that flew 500km towards Japan on August 24.

That launch, which was widely condemned, marked what weapons analysts described as a clear step forward for North Korea's nuclear-strike ambitions.

China is North Korea's only major ally, but ties between the neighbours have frayed amid a number of nuclear and missile tests and what many outsiders see as other provocations in recent years.

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

The UN Security Council in late August 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.

North Korea: Long-range missile launched amid sanctions

Source: Al Jazeera News and agencies