Envoys from China, Japan, North Korea, Russia, South Korea and the US began meeting at 02:30 GMT as scheduled, said Ding Yonghua, a Chinese foreign ministry official.
The US, Japan and South Korea earlier held three-way talks for an hour to discuss tactics after the US and South Korea both held meetings yesterday with North Korea.
"They evaluated and exchanged opinions about each keynote speech made yesterday and they also fine-tuned positions on various issues," said South Korean foreign ministry spokesperson Shin Bongkil.
South Korea's Yonhap news agency said the three nations considered a proposal presented by Pyongyang yesterday.
In it, North Korea said it was willing to give up its nuclear ambitions if the US resumed fuel supplies cut off in December, the JoongAng newspaper in Seoul said.
It would also resolve concerns about its missile development if diplomatic ties with the US and Japan were normalised.
In addition, North Korea would scrap its nuclear programme when a US-led consortium completes the construction of two light-water nuclear reactor in the Stalinist state.
The US has been adamant that the regime's nuclear programmes must be completely dismantled before it considers economic assistance and diplomatic normalisation.
Shin said the US side also briefed South Korea on its bilateral contact with North Korea yesterday, referring to a 30-minute meeting between US envoy James Kelly and Pyongyang's chief negotiator Kim Yong-Il.
Kelly also sat next to Kim at a 90-minute formal dinner and the two talked via interpreters for about 60 minutes, according to South Korean officials present who did not say what they discussed.
Shin said South Korea informed the US side on Inter-Korean contact made yesterday.
North Korea requested a meeting with the South after a dinner hosted by Chinese Foreign Minister Li Zhaoxing because they did not fully understand what Kelly had said in his opening address.
"There were some parts of the US keynote speech North Korea could not understand properly," said Shin, highlighting the difficulties of interpretation with five languages being used in the talks.
"Our side explained it to North Korea and they said they understood that," he said, without going into details of exactly what the North had trouble comprehending.
According to the White House, Kelly used his formal opening remarks to reiterate Washington's goal: "the complete, verifiable and irreversible elimination of North Korea's nuclear weapons programme".
State Department deputy spokesperson Philip Reeker refused to confirm Japanese media reports that the US delegation had refused North Korea's demand for a non-aggression pact.
Shin said further one-on-one Inter-Korean contact was likely today to iron out any other further misunderstandings.
Pyongyang had initially insisted on discussing the nuclear standoff only with Washington, but agreed to the multilateral talks on condition that the two countries discussed the issue bilaterally as well.
Kelly, who sparked the crisis last October by saying North Korea had admitted having a secret nuclear program in violation of a 1994 bilateral accord, has made no comment so far.
North Korea reponded to Kelly's remarks at the time by expelling UN nuclear inspectors and re-starting a mothballed nuclear reactor.
It also withdrew from the Nuclear Non-Proliferation Treaty.
Washington believes North Korea diverted enough plutonium for around two nuclear weapons prior to the 1994 accord and could produce half a dozen more within months from reprocessed spent fuel. – Sapa.