China on Tuesday lodged a formal protest with Sudan over the capture of 29 Chinese workers by rebels, after dispatching a team to the African nation to help secure their release.

The foreign ministry also called for the release of the workers, who were taken away when rebels in Sudan's South Kordofan state attacked their camp on Saturday.

Vice Foreign Minister Xie Hangsheng on Tuesday summoned a top level Sudanese embassy diplomat and lodged "urgent representations" over the incident, according to a statement on the ministry's website.

"China urges Sudan... to continue to go through every channel to expand the scope of the rescue and do everything it can to ensure the safety of the Chinese personnel," Xie said.

Sudan must also "do all it can to create conditions for their safe release and at the same time adopt measures to ensure the safety of other Chinese personnel and enterprises in Sudan," he added.

Foreign ministry spokesman Liu Weimin called "on all sides to remain calm and exercise restraint, ensure the safety of Chinese personnel and quickly release the Chinese personnel out of humanitarian concerns".

Meanwhile, the six-member team dispatched by Beijing arrived in the Sudanese capital of Khartoum to help resolve the standoff.

Team leader Qiu Xuejun told state-run news agency Xinhua they were there to help the embassy with the rescue operations and to hold consultations with Sudanese authorities.

Rebels holding the workers said they were ready to talk with the Chinese delegation.

"Why not ?" Arnu Ngutulu Lodi, spokesman for the Sudan People's Liberation Movement-North (SPLM-N) in South Kordofan state, told AFP.

"We are not fighting the Chinese. We are fighting the Sudanese government. We don't have a problem talking to the Chinese or whomever."

Lodi said from Kenya that he was not sure whether the Chinese had made contact with anyone in his movement.

The Chinese workers have been described as hostages by the Sudanese military but rebels say they were only side victims of fighting with government troops.

Sudan's army spokesman, quoted by the official SUNA news agency, vowed to free the 29 Chinese.

There is growing international concern over the situation in South Kordofan, where the government is fighting ethnic minority insurgents once allied to the former rebels who now rule South Sudan.

The South gained independence from Khartoum in July last year after decades of civil war.

The Chinese workers were involved in a road-building project in South Kordofan, and while 29 remain captive, 17 others have been moved to safety by the Sudanese army, Xinhua has said.

China is Sudan's major trading partner, the largest buyer of Sudanese oil, and a key military supplier to the regime in Khartoum.