Speculation looms that North Korea may conduct its sixth nuclear test next month in a show of force to South Korea and the United States.

A diplomatic source in Beijing said on Monday there is growing possibility based on excavation work under way at two tunnel entrances at the North’s Punggye-ri nuclear test site.

The source explained that significant evaluation and judgement is still required to figure out whether the North will use both of the entrances for a nuclear test at the same time or consecutively, and what nuclear materials will be used. 

The source pointed out that Pyongyang is ready to conduct a nuclear test any time using any excuse, and that Seoul and Washington are closely watching its movements. 

While a test could come soon, the source said it's uncertain whether it will happen around the China-U.S. summit set for early next month or April 15th to celebrate the birthday of the late North Korean leader Kim Il-sung. The source also predicted the test could be conducted around April 25th, which marks the anniversary of the foundation of the North Korean People’s Army.