North Korea's first nuclear test of 2017 could take place between October 16 and November 7, South Korea's Yonhap news agency reported, citing lawmakers briefed by the National Intelligence Agency (NIS).

Preparations for a nuclear test have been completed at North Korea's Punggye-ri test tunnel, where six underground nuclear tests were conducted from 2006 to 2017, the South Korean news agency reported.

The timing of the test will likely be determined by events in China, Pyongyang's main ally, and the United States, its biggest rival, Yonhap added.

"If North Korea conducts a nuclear test, it could be between the 20th Congress of the Chinese Communist Party on October 16 and the US mid-term elections on November 7," spokesman Yoo Sang-bum told the news agency.