The United Nations Security Council on Wednesday pledged to immediately start working on a new draft resolution for "further significant measures" against North Korea, which claimed to have tested a hydrogen bomb despite worldwide opposition.

"The members of the Security Council ... recalled that they have previously expressed their determination to take further significant measures in the event of another DPRK (North Korea) nuclear test," Reuters quoted UN Ambassador and Security Council President Elbio Rosselli as saying.

"In line with this commitment and the gravity of this violation, the members of the Security Council will begin to work immediately on such measures in a new Security Council resolution," he said.

United Nations Secretary-General Ban Ki-moon also condemned the hydrogen nuclear test by North Korea on Wednesday morning. "I demand the DPRK cease any further nuclear activities," AFP quoted him as saying.

Pyongyang on Wednesday announced that it "successfully" conducted an underground test of miniaturised H-bomb. 

"The first H-bomb test was successfully conducted in Juche Korea at 10:00 on Wednesday, Juche 105 (2016), pursuant to the strategic determination of the WPK," said the statement, translated and shared on Twitter by VOA News bureau chief.

The explosion reportedly triggered a 5.1 magnitude earthquake 19 kms from the nation's nuclear test site Punggye-ri, where North Korea has conducted such tests in the past.

"We suspect a man-made earthquake and are analysing the scale and epicentre of the quake with the geoscience and mineral resource institute of South Korea," The Guardian quoted a South Korean Meteorological Administration as saying.

Pyongyang conducted three nuclear tests at Punggye-ri site before: one in October 2006, another in May 2009 and then in February 2013. The UNSC has since reportedly approved sanctions against North Korea for violating its nuclear and missile proliferation activities.

North Korea attracted criticism from the United States, South Korea, China and several other countries for violating UNSC resolutions by conducting the nuclear test on 6 Janaury, 2016.

South Korea, others sceptical of North Korea's claim

South Korea on Wednesday questioned Pyongyang's claims of having tested an H-bomb. South Korean intelligence reportedly said that the device may not have been an H-bomb. South Korea's meteorological agency Korean Meteorological Administration also said it did not detect any radiation from the test, Reuters reported.

Bruce Bennett, an analyst for the RAND Corporation -- an American nonprofit global policy think tank -- reportedly said the explosion would have been far greater if they had detonated an H-bomb.

"The bang they should have gotten would have been 10 times greater than what they're claiming," BBC quoted Bennett as saying.

The United States and weapons experts also expressed doubts on North Korea's claims of having tested a hydrogen bomb.