The quake hit shortly after 8am with an epicentre 33 kilometres north-west of Herat city, capital of the province of the same name, and 8km below the surface, the US Geological Survey said.
It was followed by a 5.5-magnitude aftershock 20 minutes later.
Mohammad Zahir Noorzai, head of the emergency relief team in Herat province, said one person died and nearly 150 others were injured. Casualty numbers might rise, as they are yet to reach all affected areas, he said.
Sayed Kazim Rafiqi, 42, a Herat city resident, said he had never seen such devastation before, with the majority of houses damaged and “people terrified”.
He was headed to the hospital to donate much-needed blood.
“We have to help in any way possible," he told Associated Press.
An AFP reporter in Herat city said most residents were still sleeping outside a week after last Saturday's quake, fearful of aftershocks flattening their homes in the night.
However, some had begun to sleep inside again.
"Herat's people are panicked and scared," said 27-year-old shopkeeper Hamid Nizami. "It's Allah's blessing that it happened during the day, people were awake."
On October 7, another 6.3-magnitude earthquake and eight powerful aftershocks jolted the same part of Herat, toppling rural homes.
The Taliban government said more than 1,000 people were killed. The World Health Organisation (WHO) on Saturday put the figure at nearly 1,400.
Days after the initial quakes, with thousands of terrified residents left without shelter and volunteers digging for survivors, another tremor of the same intensity killed one person and injured 130 others.
The quakes were followed by dust storms, which damaged the tents in which survivors were living.
"Many of our countrymen don't have any place to live and nights are getting colder," said shopkeeper Mr Nizami.
The WHO says nearly 20,000 people have been affected by the string of disasters, with women and children making up most of the death toll.
Thousands of residents are now living around the ruins of homes where entire families were wiped out in an instant.
Mohammad Naeem, 40, said he lost 12 relatives, including his mother, after Saturday's earthquakes.
"We can't live here any more. You can see, our family got martyred here. How could we live here?"
Earthquakes are frequent in Afghanistan. In the west and centre of the country they are caused mainly by the Arabian and Eurasian tectonic plates jutting against each other.
Providing shelter on a large scale will be a challenge for Afghanistan's Taliban authorities, who seized power in August 2021 and have fractious relations with international aid organisations.
"That area is very cold, staying there after the evening is very difficult," said Public Health Minister Qalandar Ebad.
"We know they could live there in tents for one month but more than that would probably be very difficult."
Most homes in rural Afghanistan are made of mud and built around wooden support poles, with little in the way of steel or concrete reinforcement.
Multi-generational extended families often live under the same roof, meaning serious earthquakes can devastate communities.
Afghanistan is already suffering a dire humanitarian crisis, with the widespread withdrawal of foreign aid following the Taliban's return to power.