The four people were confirmed dead at a fish market that collapsed in Cebu in the central Philippines, the country's second most important trading and economic city.
The quake struck at 08:12 local time (0012 GMT) five kilometres (three miles) east of Balilihan, in the Bohol region of the archipelago, at a depth of 20 kilometres (12 miles), the agency said.
The town lies across a strait of about 60 kilometres from Cebu.
Cebu and surrounding areas impacted by the quake were among the Philippines' most popular tourist destinations.
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Photos on social media showed extensive damage to old churches and modern buildings, including a university, while major roads had also been torn apart.
Patients streamed out of one of Cebu's major hospitals, which was damaged. Local media reported one floor of the building caught fire.
The quake was followed by at least four aftershocks that measuring more than 5.0 in magnitude. The USGS initially reported the quake as having a magnitude of 7.2, but shortly afterwards lowered it to 7.1.
The Pacific Tsunami Warning Centre did not issue a Pacific-wide tsunami threat.
Balilihan has a population of around 18,500, according to the town's official website.
The Philippines lies on the so-called Pacific ring of fire, a chain of islands that are prone to quakes and volcanic eruptions.