Seven Chinese workers were kidnapped in the morning attack at the oil installation in a disputed region near the Somali border, Xu Shuang, the general manager of Zhongyuan Petroleum Exploration Bureau, told The Associated Press.
The oil company official did not give the nationalities of the workers killed, but in an earlier statement he said the vast majority of them were Ethiopians.
China has increased its presence in Africa in recent years in a hunt for oil and other natural resources to feed its rapidly growing economy. Its forays into areas considered politically unstable, however, has exposed Chinese workers to attacks.
An Ethiopian rebel group claimed responsibility for the attack.
The Ogaden National Liberation Front said in a statement sent to The Associated Press they had launched "military operations against units of the Ethiopian armed forces guarding an oil exploration site," in the east of the country.
The group has been fighting a low-level insurgency with the aim of creating an independent state for ethnic Somalis. Somalia lost control of the region in a war in 1977.
The rebel group also has been fighting Ethiopian troops inside Somalia, where Ethiopia has been backing the government in crushing an Islamic movement and re-establishing control over the country.
In Nigeria, armed militants seeking a greater share of that country's oil wealth kidnapped nine Chinese oil workers in January, and two more in March. Two were still being held, though hostages are normally released unharmed in Nigeria after a ransom is paid.
Also in March in Nigeria, five Chinese telecommunications workers were abducted for two weeks.