The two-day meeting in northeast China's Shenyang city, near the North Korean border, is addressing what Pyongyang should do to declare and disable its nuclear weapons programmes.

"We will focus our energy on discussing how to move forward the process of Korean peninsula denuclearisation," chief Chinese envoy Wu Dawei said as the talks kicked off at the Liaoning Friendship Hotel.

The so-called "declare-and-disable" phase is the second step in a six-nation accord signed in February under which the North, one of the world's most impoverished countries, agreed to end its nuclear weapons programmes.

In return, it would receive fuel aid, security guarantees and diplomatic concessions.

North Korea honoured its initial commitments last month by closing its main nuclear reactor at Yongbyon and opening its doors to UN International Atomic Energy Agency inspectors.

Chief US envoy Christopher Hill has repeatedly emphasised the need for a "declaration," meaning a complete North Korean list of its nuclear arms-related activities.

Hill insisted this week that the reclusive communist nation must come clean on all nuclear weapons programmes for the process to move forward.

The United States suspects the North, which conducted its first atomic weapons test last October, is running a secretive highly enriched uranium programme in addition to projects it has already admitted to.

"I think the uranium enrichment process needs to be addressed in the context of the declaration of programmes, and I think we have an ongoing effort to do that. I can't be more specific at this time," Hill said.

In addition, no one outside North Korea is exactly sure how much nuclear-bomb material was made at the Yongybyon plant before it was shut down.

But the US envoy was cautiously optimistic about the progress that could be made at the talks in Shenyang, about 200 kilometres (120 miles) from the North Korean border.

The talks are considered vital to enabling further progress in the next round of full six-nation disarmament meetings in Beijing, tentatively set for early September.

"What we are trying is to make sure we have a common understanding," Hill said.

The negotiations group North and South Korea, China, Japan, Russia and the United States.

The talks take place amid a domestic crisis for North Korea, which has been hit by devastating floods that have affected up to 300,000 people.

"It's a serious humanitarian issue, and we would like to be a part of the effort to assist. So we need evaluate the situation and see what we can do to help," Hill said.