The action taken by the Pacific nations, known as the Parties to the Nauru Agreement, was announced at a meeting of the Western and Central Pacific Fisheries Commission.
The ban is the latest move in a long-running battle to protect stocks of bigeye and yellowfin tuna.
The ban is aimed at the powerful distant water fishing nations such as China, Japan, Taiwan, South Korea and the United States.
From 2011, their purse seine fishing vessels will be excluded from the high seas in an area of the central Pacific, stretching between 10 degrees north of the of the equator and 20 degrees south.
Vessels that fail to comply will be refused a licence to fish in the much larger exclusive economic zones of the 8 countries.
A spokesperson for the Parties to the Nauru Agreement, Maurice Brownjohn, said unilateral action was necessary because the Western and Central Pacific Fisheries Commission had failed to act to conserve the tuna.
He says the extended ban on high seas fishing will have long-term economic benefits for the Pacific Islands because it will mean fishing can only take place under licence within their exclusive economic zones.
"At the moment running into the high seas, facilities a lot of misreporting and makes it very hard to govern and manage the fisheries," he said.
"Within the economic zones where the fishing will be restricted now, there are other measures by the parties including vessel monitoring system...and also compulsory transhipments at port, no transhipments at sea."
"Ultimately, we are brining control and proper governance under the fishery."
The Secretariat of the Pacific Community's chief tuna scientist, John Hampton, says the new ban will help prevent further decline in the vulnerable fish stocks.
"It addresses the issue of the overfishing of big-eye and in particular reducing the level of big eye taken as smaller juvenile sizes," he said.
"Likewise with yellowfin reducing the catch of yellow fin at those smaller sizes would appear to be quite important both in terms of sustainability of those stocks but also maximising the economic value of the fisheries."