The quake hit at a depth of 35km in the Molucca Sea between the Sulawesi and Maluku island groups in the early morning, the USGS said.
The Hawaii-based Pacific Tsunami Warning Center (PTWC) said hazardous tsunami waves were possible within 1,000km of the epicentre along the coasts of Indonesia, the Philippines and Malaysia.
Waves of 30cm were recorded within 30 minutes of the quake in North Maluku province north of the island of Ternate, Indonesia’s BMKG geological agency said in a statement.
Twenty-centimetre waves were logged in Bitung in northeastern Sulawesi.
Ternate resident Budi Nurgianto, 42, said he was inside his house when the tremor struck, sending people panicking outside.
“The quake was felt strongly. I heard it first from the walls of the house that shook,” he said.
“When I went outside, there were many people outside. They were panicked. The quake was felt (for) quite long, more than a minute.
“I even saw some people leaving their house without having finished their shower.”
An AFP journalist in Manado on Sulawesi, about 300km west of Ternate by sea, said the shaking woke him and others in the city of around 450,000 people.
“I immediately woke up and left my house. People (were) immediately scrambling outside. There is a school and the pupils rushed outside,” he said.
The shaking persisted for “quite long” but he did not witness “significant damage”, he added.
The PTWC said tsunami waves “reaching 0.3 to 1 meters above the tide level” were possible for some coasts of Indonesia.
Smaller waves could also reach Guam, Japan, Malaysia, Palau, the Philippines and Taiwan.
“Government agencies responsible for threatened coastal areas should take action to inform and instruct any coastal populations at risk,” the PTWC said in a statement.
“Persons located in threatened coastal areas should stay alert for information and follow instructions from national and local authorities.”
The Malaysian Meteorological Department (MetMalaysia) said in a Facebook post that the quake posed no tsunami threat to Malaysia.
“MetMalaysia is monitoring the situation,” it added.