A search was under way for the men, the diplomat said on condition of anonymity because he was not authorized to speak to the press. Several workers were not taken and managed to inform authorities, he added.
The rebels, along with many international rights activists, accuse China of indirectly funding Khartoum's war effort in Darfur through massive investment in Sudan's oil industry.
China buys two-thirds of Sudan's oil exports, and oil sales account for 70 percent of the African country's export revenue.
Darfur rebels attacked the Chinese-run Defra oil field in Kordofan last October, kidnapped two foreign workers and gave Chinese and other oil companies a week to leave the country.
Two months later, Darfur rebels attacked an army garrison in another Chinese-run oil field in the same province.
Some 140 Chinese engineers and troops are also deployed in Darfur and were among the first reinforcements sent by the United Nations, which took over peacekeeping in the western Sudanese region in January.
The Sudanese government quickly approved the Chinese contingent, even as it vetoed contributions from other countries because they were not African - including a Scandinavian engineering corps.