Japan is capable of going nuclear "virtually overnight," U.S. Vice President Joe Biden said, as he spoke about a conversation he had with Chinese President Xi Jinping in which he urged Beijing to do more to rein in North Korea.

In an interview with PBS aired Monday night, Biden said that China has "the single greatest ability to influence North Korea by cutting off A, B, C, D, a whole range of things, but it also could cause the implosion of North Korea."

"When I tell President Xi, you have to understand we got a guy up there in North Korea who is talking about building weapons that can strike, nuclear weapons strike the United States and not only Hawaii and Alaska, but ... the mainland of United States," Biden said.

"And I say, so we're going to move up our defense system, and he says no, no, no, wait a minute, my military thinks you're going to try to circle us. I said, 'What would you do? What would you do? Do you think we should stand back?'" he said. "And what happens, what happens if we don't work out something together on North Korea? What happens if Japan, who could tomorrow, could go nuclear tomorrow? They have the capacity to do it virtually overnight."

Japan possesses more than 47 metric tons of separated plutonium, which is equivalent to about 6,000 nuclear bombs. The country is allowed to reprocess spent nuclear fuel for plutonium.

Experts say Japan can build nuclear bombs in a short period of time.

Biden didn't say when that conversation with Xi happened.

But he said in a speech at a Center for a New American Security conference Monday that he spent more time with Xi than any other world leader, spending more than 25 hours of one-on-one private dinners with him under an arrangement that Xi's predecessor, Hu Jintao, and President Obama set up "for us to get to know one another."

"I remember him asking me why we were doing what we were doing in the Pacific. I said because we are a Pacific power. We will remain a Pacific power. And I suggested that our being present was one of the reasons why they have been able to progress so much because of the stability that has been sustained as a consequence of our presence," Biden said in Monday's speech. (Yonhap)