Hundreds of fuel vehicles exploded close to Afghanistan's border with Iran on Saturday, injuring dozens of people.
The fire tore through a customs post in the border town of Islam Qala, disrupting power supplies and causing millions of dollars of damage.
Video obtained by Reuters showed thick plumes of black smoke rising into the air.
Iranian authorities sent ambulances and fire engines across the border to help tackle the blaze, which as of Saturday had reportedly been brought under control.
NATO-led personnel in Afghanistan were also asked to help contain the fire.
A western official monitoring the situation told Reuters at least 60 people had been injured.
Afghan officials gave a lower casualty toll, but said that number could rise.
Iranian state media reported that about 500 vehicles had been burnt.
Officials said the cause of the fire was not immediately clear.
Initial reports suggested the blaze started after a gas tanker exploded.