The Chinese special envoy, former foreign minister Tang Jiaxuan, handed a personal message from President Hu Jintao to reclusive North Korean leader Kim Jong-Il, a foreign ministry spokesman in Beijing said.
"This is a very significant visit against the backdrop of major changes in the situation on the Korean peninsula," spokesman Liu Jianchao said.
The encounter between the Chinese envoy and Kim is thought to be the North Korean leader's first announced meeting with any foreigner since Pyongyang shocked the world with its October 9 test of a nuclear weapon.
China, North Korea's closest ally and by some way its largest aid donor and trade partner, is seen as critical to ensuring United Nations sanctions imposed after the test are made to bite.
Asked by reporters in Seoul, Rice said she had not heard what came out of the meeting in Pyongyang.
"I hope it has been successful in conveying to North Korea that there is really only one path," she said, referring to the dismantling of its weapons programmes.
A senior US official travelling with Rice earlier said the Chinese delegation would likely send a "very strong" warning against further nuclear tests.
Rice warned of "grave consequences" if the Stalinist regime conducted a second test while also stressing that the door to negotiations remained open.
The top US diplomat arrived in Seoul from Tokyo on Thursday on a four-nation tour aimed and bolstering allies' resolve to enforce the sanctions against North Korea embodied in UN Security Council resolution 1718.
South Korea promised Rice it would carry out a "full scale" review of its economic ties with the North in light of the UN sanctions, a senior US official said.
President Roh Moo-Hyun and Foreign Minister Ban Ki-Moon told Rice they would bring their government's "sunshine" policy of engagement with the North into line with the UN measures, the official said.
While details of specific projects in the North were not discussed, the Koreans said they were "engaged in a full-scale evaluation of the entire range of North-South relations".
"They are looking at all of the aspects of their relationship and will be announcing how they will comply with 1718 in the very near future," he said on condition of anonymity.
The resolution calls on North Korea to return to negotiations over its nuclear programme and imposes a range of financial, trade and military restrictions.
While Japan assured Rice in meetings on Wednesday that it fully supported the sanctions, South Korea and China have balked at taking measures that could cause the collapse of their impoverished neighbour.
Rice, who earlier held talks in Japan, travels on to China on Friday and then Russia on Saturday as part of the US drive to tighten the pressure on Kim's isolated regime.
During her talks here, Rice sought to ease Seoul's concern that sanctions, notably the inspection of cargo to and from the North, could lead to conflict with Pyongyang, which has branded the measures a declaration of war.
"The US has no desire to do anything to escalate tensions," she said at a joint press conference after talks with Foreign Minister Ban, who is also the incoming head of the United Nations.
"We want to leave open the path of negotiation," Rice said. "We don't want the situation to escalate."
But she and Ban warned of "grave consequences" if the North carried out a threat to stage a repeat test.
"We agreed that it would aggravate the current situation and that it should never take place," Ban said. "We agreed that in case it happens, there should be more grave consequences."
Rice and Ban later went into three-way talks with Japanese Foreign Minister Taro Aso.
North Korea has boycotted six-nation disarmament talks -- involving China, Japan, Russia, the United States and the two Koreas -- since last year after Washington took action to lock it out of the international banking system.

Copyright AFP (Agence France-Presse), 2006