The Niger Delta region has become notorious for kidnappings by separatists seeking a share of its oil wealth.
Nigerian officials said shortly after the Chinese were taken hostage that they had established contact with the armed men and were in negotiations.
They did not announce the identity of the abductors or their demands.
The incident had prompted China to lodge a formal complaint with the Nigerian government.
Media reports had previously quoted Xu Jianguo, China's ambassador to Nigeria, as saying the abductees were employees of Sichuan Telecommunications Company.
Earlier on Thursday Nigerian separatists released Roberto Dieghi, one of three Italian oil workers taken hostage in early December.
The Movement for the Emancipation of the Niger Delta (Mend) said it would keep two other Italians and one Lebanese who were kidnapped during the same raid.
The group said in an email: "This release ... had absolutely nothing to do with Roberto Dieghi's poor state of health. The release of Mr Dieghi is an act of goodwill on our part which we hope will be reciprocated by the Nigerian government.
"There are no discussions ongoing with regard to the release of the remaining two Italians and one Lebanese still in our custody. They are being held indefinitely."
Mend, who are demanding the release of a separatist leader and a larger share for southern Nigerians in oil revenues, denied any responsibility for taking the Chinese hostages.