Wu Dawei said the six-nation talks on ending North Korea's nuclear program were experiencing ups and downs, and "we are gradually overcoming these ups and downs," Wu told reporters.
Asked how long that would take, Wu replied, "Around the autumn."
Progress in the talks has sputtered over North Korea's pledge to provide a full inventory of its nuclear activities and facilities. While Pyongyang insists it provided a list in November, the United States says it was incomplete.
The main sticking points are believed to be what North Korea will reveal about any nuclear know-how or materials it provided to other nations, along with allegations it had a secret uranium enrichment program in addition to its known plutonium program.
Wu met earlier Wednesday with U.S. Assistant Secretary of State Christopher Hill, who traveled to Beijing to discuss progress after talks with the top North Korean negotiator, Vice Foreign Minister Kim Kye Gwan, in Singapore the day before.
China is host of the six-nation talks and Wu serves as the chairman.
"I want to stress that we haven't yet arranged for all the factors, all the elements that we need to be put together," Hill told a news conference Wednesday at the U.S. Embassy.
"We have a lot of work ahead of us. I don't want to suggest we've had any major breakthroughs," Hill said.
Hill said the talks with Kim in Singapore had been productive, but declined to discuss details.
"All in all I would say it's been a good couple of days," Hill said. He declined to comment on how far away an agreement remained.
South Korea's Yonhap news agency quoted Kim as saying after the Tuesday meeting that differences between the two sides "have been narrowed a lot."
Kim made no public comments after arriving in Beijing later on Wednesday for consultations.
However, the North's Foreign Ministry said Wednesday that its negotiators had reached a "consensus" with Hill in Singapore on American political concessions in return for the declaration.
No details were given, but according to an original understanding, the North was to receive diplomatic rewards, including removal from U.S. terrorism and sanctions blacklists as well as fuel oil.
North Korea began disabling its main nuclear facilities last year in exchange for aid and diplomatic concessions.
Hill has said that once a new list is submitted, it will be handed to the Chinese hosts and discussed at a meeting of the six nations.
China is North Korea's main diplomatic ally and source of food and energy assistance.