A new round of talks aimed at disarming North Korea will focus on verifying the North's own account of its nuclear programmes, the chief U.S. envoy said on Thursday.

The negotiations are the first in nine months, after North Korea last month produced a long-delayed declaration of its nuclear activities, one of the initial steps pledged under a disarmament deal.

"Obviously we're going to focus very much on a verification regime to wrap up this phase," U.S. envoy Christopher Hill told reporters.

"We've been discussing that with all the partners in the process, so I don't think there will be any surprises," he said.

China's North Korea nuclear pointman, Wu Dawei, told the opening session of the talks that he was encouraged by the fact the process was getting under way again.

"It is encouraging to see in the past three years, despite twists and turns, all of us are sharing the same boat and walking the same path," Wu said.

"We overcame various difficulties on the way forward. No matter what the difficulties were, these difficulties made us smarter and stronger."

The talks, which group North and South Korea, the United States, Japan, Russia and host China, are scheduled to run for three days in the Chinese capital.

Over the course of the long-running negotiations, the parties have induced North Korea to freeze its Yongbyon nuclear reactor and begin steps to dismantle it, in exchange for energy aid and the promise of improved diplomatic relations.

But despite finally winning the declaration, questions remain about North Korea's murky nuclear programme, particularly U.S. suspicions Pyongyang is secretly working to enrich uranium.

Hill said that given consultations between rounds of talks, there should be no surprises about what verification entails, but the South Koreans have suggested the North was still at odds with the other countries about how to verify its statement.

"As everybody would when you are going into negotiations, we do have hopeful expectations," South Korean envoy Kim Sook told reporters. "But realistically, this is a very difficult process, with each of the countries having its own position."

Kim said Thursday's talks would set out the agenda for this round, with more substantive discussions expected on Friday.