The first earthquake, at 6.0 magnitude, struck at a depth of 10 kilometres.
A 6.5-magnitude earthquake hit off the coast of the Pacific nation of Vanuatu on Friday, just hours after another strong tremor in the same area, but no tsunami alerts were issued.
The first earthquake, at 6.0 magnitude, struck at a depth of 10 kilometres (6 miles) some 86 kilometres from the town of Port Orly, the United States Geological Survey said.
This was followed several hours later by the stronger aftershock at the same depth and in the same area.
"Based on all available data, there is no tsunami threat from this earthquake," the Pacific Tsunami Warning Center said of the most recent tremor.
There were no immediate reports of any damage.
It follows a series of quakes in the region over the past week, including a 6.9 magnitude one, also close to Port Orly on Espiritu Santo island. No damage was reported.
Vanuatu is part of the "Ring of Fire", a zone of tectonic activity around the Pacific that is subject to frequent earthquakes and volcanic eruptions.