China will send 700 soldiers to a United Nations (UN) peacekeeping force in South Sudan later this year to protect civilians amid a rebellion in the African country, a UN official said on Wednesday, denying a report they were already being deployed.

The Wall Street Journal had quoted a spokesman for South Sudan's president as saying the airlift of a Chinese infantry battalion to the South Sudanese states of Unity and Upper Nile was under way and would be completed in several days.

READ: China deploys troops to UN force to protect South Sudan oilfields

Joe Contreras, the acting spokesman for the UN mission in South Sudan (UNMISS) said no date had been finalised, nor the deployment area. Contreras also denied peacekeepers were protecting industry infrastructure in oil-rich South Sudan. China is the biggest investor in the country's oil industry.

"Nowhere in the current mandate and mission does it say that peacekeepers will be asked to defend oil industry installations. When circumstances arise ... our peacekeepers will be called upon to protect civilian oil industry workers but not the refinery or pipeline or storage tanks," Contreras said.

Any participation by Chinese peacekeepers was in accordance with UN Security Council authorisation and was only to maintain peace and stability, Chinese Foreign Ministry spokeswoman Hua Chunying said in Beijing.

China is willing to increase its support for South Sudan peacekeeping in line with Security Council requests, she told a daily news briefing. "We are currently in close communication with the United Nations secretariat," Hua said, adding that China now has more than 1,800 peacekeepers in Africa.

UN officials have previously said it would be the first time China had contributed a battalion to a UN peacekeeping mission. Last year China sent a smaller "protection unit" to join a UN mission in Mali.

China has played an unusually active diplomatic role in South Sudan.

Chinese officials have been in regular contact with Western diplomats to help African mediators push for a halt to fighting in the country. China has also pushed rival factions loyal to President Salva Kiir and rebel leader Riek Machar to talk.

Around five per cent of China's oil imports came from South Sudan when it was pumping at full tilt. The state firm China National Petroleum Corp has a 40 per cent stake in a joint venture developing the country's oil fields.