The accident occurred in Ghazni’s Muqur district, which links capital Kabul to the southern provinces.
The ill-fated buses had been part of a daily convoy ferrying passengers to the Kandahar province.
Eyewitnesses said the oil tanker had been brimming with fuel which burst into flames immediately after the collision.
Ameenullah Amerkhel, Ghazni’s security chief, said the accident took place at around 7:30am.
According to local officials, an estimated 125 passengers had been on board the doomed buses.
More than 70 people were reportedly killed in the accident, while more than 50 others were injured.
Local medical sources fear the death toll may rise further, as most of those injured are in critical condition and have been taken to Kabul for emergency treatment.
An investigation has since been launched into the deadly accident.
The exact cause of the collision has yet to be determined, but most observers believe it was the result of reckless driving by the drivers who often remain behind the wheel for exhaustingly long hours, in addition to Afghanistan’s poorly regulated traffic system.