The killings were reported at the China Petroleum & Chemical Corp.'s Zhongyuan Petroleum Exploration complex in Abole, about 75 miles from Jijiga, the capital of Somali state, near the Somali border.
Oil company acting manager Xu Shuang told Xinhua that 200 gunmen attacked the site early Tuesday. He said there was a 50-minute firefight between the gunmen and about 100 soldiers protecting the field. Later, he said, the gunmen took control of the site, which employs about 37 Chinese workers and more than 120 Ethiopians.
It was unclear if the killings occurred after the gunmen took control of the premises. There also was no immediate confirmation on the identity of the gunmen.
Xu said the gunmen kidnapped seven Chinese workers, Xinhua reported.
An Ethiopian press official was quoted as saying Prime Minister Meles Zenawi ordered the defense ministry to send immediate reinforcements to the area.
The Chinese Embassy in Addis Ababa set up an emergency team to coordinate with the Ethiopian government and the military, a spokesman told Xinhua.