“Based on the latest reports from the scene, the quake killed five people and injured 12 others,” South Khorasan Crisis Management Headquarters Director Mohammad Ali Akhoundi told Mehr news agency.
Many in the provincial capital Birjand fled their homes, the agency said.
Iran has been frequently hit by quakes – in 2003 tens of thousands of people were killed in a quake which flattened Bam.
More than 300 people died in two quakes in north-western Iran in August this year.
Tehran University’s Seismological Centre said the latest quake hit at 20:38 local time (17:08 GMT), 25km (15 miles) from Zohan.
State TV quoted a local MP, Javad Heravi, as saying it had damaged rural buildings and cut phone and power lines. Twelve villages were affected, the TV added.
The epicenter of the quake was 25 kilometers (15 miles) from the town of Zohan, at a depth of nine kilometers, the Iranian Seismological Center said on its website.
Javad Heravi, who represents the province in the Iranian parliament, said that the quake caused damage to rural buildings and cut power lines and telephone communication.
Iran is located on seismic fault lines and is prone to earthquakes, experiencing at least one small tremor per day on average.
In December 2003, about 27,000 people were killed and 30,000 others injured when a 6.6-magnitude earthquake shook the historic city of Bam in southeastern Iran.
The deadliest earthquake in modern Iranian history was a 7.4-magnitude tremor that occurred on June 21, 1990 and affected Gilan and Zanjan provinces. About 40,000 people were killed, 60,000 others were injured, and around 100,000 adobe houses sustained major damage or collapsed.
According to the U.S. Geological Survey, there have been 197 2.5-magnitude or higher seismic events worldwide during last seven days.
The Guardian Express will update events in Iran as soon as they’re made available to us.
D. Chandler contributed to this report