They were seized yesterday by gunmen who held up their convoy that was under a police escort near Calabar, the capital of southeastern Cross River state, said police Commissioner Jimoh Ozi-Obeh.
Another Australian escaped, Australian Foreign Minister Julie Bishop said.
"A very intense search is on, with more patrol and surveillance teams dispatched to the rescue," Ozi-Obeh told The Associated Press.
Nigerian newspapers quoted witnesses saying the hostages were forced onto a boat, meaning they could be anywhere in a maze of estuaries and mangrove swamps that dominate the state's geography.
Kidnapping for ransom is common in Nigeria but generally involves no fatalities. Hostages are returned unharmed once money exchanges hands, though a German construction worker was killed in southwestern Nigeria late last year by gunmen who kidnapped a second German. He was later released.
Ozi-Obeh identified the foreigners kidnapped as Australians Jack Countentz, Mark Gabberdy and Peter Zoutenbier, New Zealander Jamal Khan and South African Wayne Smith.
New Zealand's Prime Minister John Key said on state TV yesterday that his government would not pay any ransom because it would potentially put a bounty on the head of any citizen.
