China's top foreign policy official on Monday made his second visit to Vietnam in four months, as the communist neighbours work to repair ties strained to breaking point by a territorial dispute.

In May, Beijing moved a deep-water oil rig into waters claimed by Hanoi, prompting a months-long high-seas standoff and triggering deadly anti-China riots in Vietnam. The rig was removed in July.

State Councillor Yang Jiechi, who last visited in Hanoi in June when he told Vietnam to stop "hyping-up" the dispute, met Foreign Minister Pham Binh Minh Monday for talks.

Vietnam's Prime Minister Nguyen Tan Dung was not present as he left earlier for India, where he is due to meet Prime Minister Narendra Modi, highlighting Hanoi's recent efforts to seek powerful allies elsewhere after relations with Beijing soured.

After the Hanoi talks, Minh said Vietnam had "always attached importance to developing its cooperative partnership with China," according to a statement released by Vietnam's foreign ministry.

"Both sides recognise that handling maritime issues well is very important for bilateral relations," the statement said, without elaborating.

Chinese foreign ministry spokeswoman Hua Chunying told a regular briefing in Beijing on Monday that bilateral ties had been hit by "temporary difficulties" but things were now back on track.

The ministry added in a statement that both sides had agreed to avoid "actions that complicate and broaden disputes".

Vietnam staunchly opposes China's ongoing efforts to develop airstrips and military bases on the island chains it controls in the South China Sea.

Its commercial fishing fleet routinely clashes with Chinese fisheries patrol vessels in contested waters from the northern Gulf of Tonkin to fishing zones around the Spratly Islands hundreds of miles further south.

It is unlikely there was any real breakthrough in resolving territorial rows during the talks, said Ian Storey, a senior fellow at the Institute of Southeast Asian Studies in Singapore.

"Nevertheless, Yang's trip to Hanoi is important because it represents another step forward in efforts by the two countries to repair their relationship which was severely damaged by the oil rig incident," he said.

After rebuffing "scores of requests" for talks over the summer, the second visit by Yang Jiechi shows a "tactical shift" by Beijing, said Jonathan London of Hong Kong's City University.

The talks are evidence that China now "seeks stability" in its relationship with Hanoi, possibly to prevent it drawing other countries such as the US into the South China Sea dispute.

Yang's visit come "within a dynamic context that includes Hanoi's warming ties with Washington and Beijing's continued efforts to change the status quo in the maritime area," he said.

Since the rig incident, Vietnam has drawn closer to its former wartime foe America, with the US partially lifting a ban on lethal weapons sales earlier this month.

Vietnam last week released a high-profile dissident whose case has been raised by US President Barack Obama and allowed him to travel to the US.