"People ran helter skelter when the attackers arrived so maybe they are hiding somewhere. There is no report of casualties [among the Chinese] and a search is under way," Ojediran added.
Police said the attackers also looted the company's field office and took an unspecified amount of money.
No one has so far claimed responsibility for the attack.
The most prominent separatist group in the region, the Movement for the Emancipation of the Niger Delta (MEND), told the AFP news agency it was not involved in the incident.
"It was likely carried out for money", the group's spokesman said in an email.
This is the second time this month that Chinese working in Africa's biggest oil-producing country have been seized.
On January 5, five employees of Sichuan Telecommunications Company working on a project to extend telephone services to rural areas were abducted from their residence.
Thousands of foreign oil workers have left the Niger delta in the past year as kidnappings of foreign workers increased dramatically.
Thirty-two foreign workers are currently being held by armed groups in southern Nigeria.
Kidnappers tend to be either criminal gangs lured by the idea of easy money or separatist groups calling for autonomy and a greater share of the country's oil wealth for the region, security experts say.
Residents of the delta complain that while the region generates 95 per cent of Nigeria's foreign currency earnings, but they have little to show for this in terms of development or living standards.