WELLINGTON, New Zealand — A magnitude 7.3 earthquake struck Tuesday just off the coast of Vanuatu in the South Pacific Ocean, the USGS said.

The quake occurred at a depth of 57 kilometers (35 miles) and was centered near Port Vila, the largest city in the island nation.

It was not immediately clear whether it caused any damage.

The jolt was followed by a magnitude 5.5 aftershock at the same location.

Vanuatu government websites were offline in the aftermath of the quake.

The USGS warned of tsunami waves for some coasts on Vanuatu, a group of 80 islands that is home to about 330,000 people.