Negotiators had been due to issue a statement on Saturday agreeing to a nuclear-free Korean peninsula and to meet again by the end of June for further talks to resolve the dispute.
But a closing ceremony scheduled for the morning had still not materialised in the afternoon, as diplomats from the United States, the two Koreas, Japan, Russia and host China huddled behind closed doors.
Statement or not, there was little evidence the diplomatic gulf between North Korea and the United States had narrowed, as negotiations stretched into the afternoon of a fourth straight day.
A diplomatic source said the North had shown some "reluctance" to accept the proposed joint statement.
North Korean demand
South Korea's Yonhap news agency quoted sources as saying Pyongyang had objected to language in one clause and proposed its own changes.
The United States had described the talks as "useful" and Russia said they were "down to earth". Diplomats said the six parties meeting in Beijing had little hope of producing anything beyond a vague consensus and an agreement to meet again.
Diplomats said a joint statement had been due to agree to a third round of negotiations by the end of June, part of a seven-item statement.
They said North Korea and the US had received instructions from home and agreed to adopt the joint statement.
"Right now, the parties are in the process of carrying out intensive consultations on a document, so the hope still exists. If there is no document, we should not say the talks were a failure"
Chinese Foreign Ministry spokesman
Japan's Kyodo news agency said the six countries would call for the "coordinated denuclearisation" of the Korean peninsula and for the parties to meet again by the end of June.
They also agreed to set up a working group to discuss the issue further.
A closing ceremony was due to be held in Beijing at 11am
(0300 GMT), but that was delayed by at least an hour. Negotiators sat down for another round of discussions just before noon on Saturday, a Japanese official said.
The crux of the dispute is a US accusation - which North Korea denies - that North Korea is pursuing a uranium enriching programme for nuclear weapons.
A Japanese diplomat said late on Friday the US had not shown any evidence the North had such a programme.
The North wants aid and a security guarantee in return for a nuclear freeze. The United States wants a complete, irreversible and verifiable dismantling of its nuclear programmes.
"We are trading an end to the nuclear programme for security assurances and in so doing, opening the possibility of the kind of approach we were prepared to take before the crisis erupted"
A US official
"Differences, difficulties and contradictions" made continuing the talks essential, China said.
But it prepared for the possibility no statement would come from the discussions, which took six months of tough diplomacy to pull together after an inconclusive round in Beijing in August.
"Right now, the parties are in the process of carrying out
intensive consultations on a document, so the hope still
exists," Chinese Foreign Ministry spokesman Liu Jianchao said
on Friday. "If there is not a document, we should not say the talks were a failure."
Officials in Washington said US negotiators outlined a series of coordinated steps that Washington could take if the North agreed to a complete, verifiable and irreversible dismantling of its nuclear programmes.
Initially, aid would come in the form of energy assistance
from other parties to the talks - South Korea, Russia and
China - but the United States would be at the table, the
Washington had previously insisted Pyongyang completely dismantle its nuclear programme before it put an offer on the table; rejected the idea of a nuclear "freeze"; and said the North would have to act before the United States acted.
"We are trading an end to the nuclear programme for security assurances and in so doing, opening the possibility of the kind of approach we were prepared to take" before the crisis erupted, a senior US official said.