People fled their homes as the quake struck and brought walls and buildings down. But others were left trapped under rubble in villages across the district of Zohan in South Khorasan province, Fars news agency said.
Iran’s Red Crescent Society dispatched 15 rescue teams to the affected areas to search for people stuck under the debris and doctors in the provincial capital of Birjand were on alert to treat those hurt, Fars new agency reported.
Rescue units of Iran’s national Basij militia also joined operations, dispatching three medical teams.
Emergency workers had reached some areas and the number of confirmed dead could rise, Tehran’s deputy emergency services director Mohammad Sarvar said.
Two villages appeared to have sustained the worst of the damage including the village of Sharaj where five people were killed, Mehr news agency quoted district governor Farhad Falahati as saying.
At least 12 aftershocks have been registered since the quake struck at 2038 local time (1708 GMT) on Wednesday, the Iranian Seismological Center said.
The centre said the epicenter was 42 km from the town of Qayen, the heart of Iran’s saffron-growing region, one of the country's major non-oil exports.
The USGS said the quake, which it initially recorded as magnitude 6.0, was very shallow at a depth of 3.3. miles. It located the epicenter as 77 km north-northeast of Birjand, near the border with Afghanistan.
Iran is crises-crossed by major fault lines and has suffered several devastating earthquakes in recent years, including a 6.6 magnitude quake in 2003 which flattened the southeastern city of Bam and killed more than 25,000 people.
In August more than 300 people were killed when two quakes struck northwestern Iran.