The aftershock occurred at 6:10 a.m., according to the USGS. No deaths have been reported in either quake, the first of which left hundreds of homes damaged or destroyed in New Zealand.
It was unclear if the most recent quake would trigger a tsunami warning for the nearby islands, as was issued after the temblor of the previous day. That warning was canceled after officials decided the quake did not pose a broad threat.
"There are some initial reports that 3,000 people have been affected," Suzy Sainovski, spokeswoman for the aid organization World Vision, said after the 7.7. "Some of these are traditional houses that are on stilts, and made with vegetation."
The larger earthquake prompted power outages and the evacuation of 20 people from a hospital on the island of Makira.
The Associated Press contributed to this report.