BEIJING (AFP) - Major Chinese oil firms have prepared evacuation plans in case spreading violence in Iraq - a key energy provider to the Asian giant - threatens their operations, state media reported on Thursday.

China has more than 10,000 workers on a wide range of projects in the Middle Eastern country, officials say, although most are in the south, far from the current fighting.

Militants from the jihadist group, the Islamic State of Iraq and the Levant (ISIL), have captured vast stretches of territory in a lightning offensive that is entering its second week.

"Most Chinese workers have gone to work as usual. But if insurgents begin to attack Baghdad, we will pull out of the country immediately," an employee of Chinese state-owned energy giant China National Offshore Oil Corp (CNOOC) told the Global Times newspaper.

Resources are a key interest for China, the world's second-largest economy, and Iraq is its fifth-largest source of crude oil imports, while China is the largest foreign investor in Iraq's oil sector. Production at the four oil fields of PetroChina, the listed arm of China's largest oil producer China National Petroleum Corp (CNPC), has not been affected, a company representative told the paper.

All of them are in central or southern Iraq, but the representative added: "Some Chinese nationals in the north were evacuated. We have prepared some contingency plans."

The Global Times also reported that more than 1,000 Chinese employees of state-run firm China Machinery Engineering Corp were "stranded" in the northern Iraqi city of Samarra, although a company representative disputed the description.

A CNPC employee was kidnapped last week from an oil field project in southern Iraq, but has since been released, Chinese foreign ministry spokesman Hua Chunying said on Wednesday. The ministry has issued security warnings and guidance to firms operating in Iraq:

"We don't want to see that the situation will come to what it was like in Libya when we had to carry a large-scale evacuation" in 2011.

"We have over 10,000 Chinese employees working in Iraq. It is to my knowledge that most of them are in relatively safe areas, instead of the conflict zones."

Beijing will "take all necessary measures to safeguard the security of Chinese citizens in Iraq", she added, depending on how the situation evolves.

In recent days, some Western embassies have begun withdrawing staff from Baghdad, and on Tuesday, Turkey said that it had evacuated its consulate in the southern Iraqi city of Basra.