Residents fled the Afghan city of Spin Boldak overnight, which lies along the 1,600-mile (2,600 km) border between the two countries.
A medical worker in the nearby city of Kandahar told BBC Pashto that four bodies had been brought to a local hospital. Four other people were wounded. Three were reportedly wounded in Pakistan.
There has been sporadic fighting between the two countries in recent months, while Afghanistan's Taliban government has also accused Pakistan of carrying out air strikes inside the country.
Both sides have confirmed they exchanged fire overnight but each blamed the other for initiating the four hours of fighting.
Border clashes have erupted again between Pakistan and Afghanistan's Taliban forces, with each sides accusing the other of breaking a fragile ceasefire.
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