The kidnapping in Port Harcourt comes a day after a US oil executive was shot dead in the city.
A rebel group waging a five-month-old campaign of attacks against the industry said it was not involved in the abduction, which police and oil industry sources attributed to a community dispute.
Industry sources said the foreigners were employees of Italian oil contractor Saipem and the Italian foreign ministry said they included at least one Italian national.
Police said one suspected kidnapper had been arrested.
An oil industry source, who asked not to be named because of his company's policy, said: "A group of expatriates were kidnapped in Port Harcourt city.
"They had mobile [armed] police escort, but the kidnappers got the mobile police out of the car and kidnapped the expatriates."
Samuel Agbetuyi, Rivers State Police Commissioner, said reports of the kidnapping were sketchy.
Nigeria is the world's eighth-
largest oil exporter
"One of those who did it has been arrested," he said.
The Movement for the Emancipation of the Niger Delta, whose attacks against the world's eighth-largest oil exporter have cut output by a quarter, told Reuters by email that they were not responsible.
Police and industry sources attributed it to a community problem.
An oil industry source said talks were already under way with the community to secure their release.
Kidnapping is a fairly common method used by impoverished villages in the lawless delta, suffering neglect from their own government, to extract benefits or cash from oil companies.
US worker killed
On Wednesday a gunman on a motorcycle shot dead a US citizen working for Baker Hughes, a Texan oil services company.
Diplomatic and oil industry sources said the killing was probably an isolated incident related to a work dispute.
Port Harcourt is the largest city in the Niger Delta, which pumps all of Nigeria's oil, and several multinationals have offices there, including Royal Dutch Shell and Agip.