According to the Iranian Seismological Center, the quake hit the town of Kaki, some 90 kilometers southeast of Bushehr, at 4:22 pm local time (1152 GMT) on Tuesday at a depth of 12 kilometers.
The quake totally destroyed one village while rescue efforts ramped up into the night nearer to the epicenter in search of survivors and to feed and house hundreds of residents who were traumatized by at least 16 aftershocks.
Many houses in rural parts of the province are made of mud bricks, which have been known to crumble easily in quake-prone Iran. Some 700 homes were destroyed.
Across the Persian Gulf, offices in Qatar and Bahrain were evacuated after the quake. The early afternoon shock was also felt in Dubai.
Water and electricity lines were severed and communities stayed in the streets because of the threat from aftershocks.