Transcript for North Korea says it successfully tested hydrogen bomb

We say good morning on this Sunday morning. Right to the breaking news overnight. A fresh provocation from knot Korea. It could be extremely concerning. The regime announcing it has carried out one of its most powerful nuclear test yet. In fact, its most powerful test yet. They claim it was an h-bomb capable of being attached to an intercontinental ballistic mis. They released this photo showing what is is described as the loading of the h-bomb into a new missile. The specific claims have not been verified. The artificial earthquake caused by the test was several times stronger than tremors from earlier tests. Reportedly it shook buildings in China and Russia. It's being reported that president trump's national security adviser had an emergency phone call overnight with his South Korea phone call. How will the president himself who has promised fire and fury, react to this news. We start with neen our London bureau. Good morning. Reporter: This is a highly provocative and dangerous move. Just over two week back, the president praising North Korea for seeminging to back down. Now it's clear Pyongyang is driven to develop a nuclear weapon that could put America within range. Overnight, the north Korean state news agency announcing what is believed to be etc. Most powerful nuclear test yet. A hydrogen bomb fitted for an intercontinental ballistic missile. The announcement coming hours after the U.S. Gs detected a 6.3 magnitude explosion near the site where all of the nuclear tests have been conducted underground. South Korea calling it an artificial earthquake. Japan saying it may have been kuzed by nuclear tests. South Korea believes it is four to five times stronger than the one dropped on nagasaki. This latest provocation highlighting the tensions over the rapid expansion of the north Korean missile program. North Korea best not make any more threats to the united States. Reporter: T president trump making a bold statement weeks ago in reaction so Kim Jong-un's statements to Guam. They will be met with fire and fury, like the world has never seen. Reporter: And just four days ago, the U.S. Joining forces with South Korea for joint military exercises, flying bombers in a show of force after Kim Jong-un launched his 21st missile since February. Even the close ally China is strongly condemning the test. South Korea wants America to deploy its strongest stra feetic assets to isolate Pyongyang. How will the president respond? One huge X factor is president trump in all this.

This transcript has been automatically generated and may not be 100% accurate.