US. Defence Secretary James Mattis has threatened a "massive military response" to any attack on the United States or its allies after North Korea conducted its most powerful nuclear test to date.

Speaking outside the White House, Mattis said: "Any threat to the United States or its territories, including Guam or our allies will be met with a massive military response, a response both effective and overwhelming."

Mattis said Washington was not looking for the "total annihilation of a country, namely North Korea. But as I said, we have many options to do so."

North Korea yesterday successfully tested what it said was a hydrogen bomb. Experts said it was 10 times more powerful than previous tests.