Their Iraqi captors threatened to kill the eight men who went missing last week, if China - a critic of the US invasion of Iraq - failed to explain why the workers were apparently building facilities for the Americans.
"China's foreign ministry and embassy in Iraq should take fast and effective measures and spare no effort to free the hostages," the official Xinhua news agency quoted President Hu Jintao and Premier Wen Jiabao as saying on Wednesday.
The captors suggested the eight, who were all from the same poor, rural county in the southeastern coastal province of Fujian, were working for a US contractor but were trying to leave Iraq after failing to find work, a foreign ministry spokesman said.
Sympathy and support
President Hu has urged Iraq to
take measures to free the men
"China is very concerned about this case. Chinese people have always been friendly to Iraqi people and have always shown them sympathy and support," spokesman Kong Quan said in a statement.
The ministry also urged Chinese nationals not to travel to Iraq.
"I feel uneasy and want nothing but his safe return," Gao Yun, the wife of hostage Lin Qiang, was quoted as saying by the China News Service.
Chen Mei, 14, the daughter of hostage Chen Qin'ai, said her father went to Iraq to earn money to support the family, particularly to help her and her two brothers go to school.
Thousands of Asians, including Chinese, are employed by private contractors working to rebuild Iraqi infrastructure and for the US military.