The first quake, with a magnitude of 7.8, struck 294 kilometres northwest of the Vanuatu island of Santo, and 596 kilometres northwest of the capital of Port Vila, at a depth of 35 kilometres.

Just 15 minutes later a second quake with a magnitude 7.3 hit at the same depth but 35 kilometres farther north of Santo and Port Vila.

The Pacific Tsunami Warning Centre immediately issued a regional tsunami warning for 11 nations and territories, including Vanuatu, the Solomon Islands, Papua New Guinea, Nauru, Fiji and Kiribati. A tsunami watch was in effect as far as Australia and New Zealand.

There were no immediate reports of injury or damage from officials in Vanuatu, a chain of 83 islands, it lies just over 2,200 kilometres northeast of Sydney, Australia.

"We have no damage reports yet, but we have had no contact with Santo so far," Vanuatu police spokesman Take Rakau told The Associated Press.

While the quakes were not felt in Port Vila, he said Santo, with its capital of Luganville, "most likely could have felt them."