The closed Torkham gate is seen from the zero point at the Torkham border crossing between Afghanistan and Pakistan. File/AFP

Pakistan's main border crossing with Afghanistan was closed for a second day on Thursday, leading to a build-up of trucks laden with goods, after clashes between security forces from the two countries.

The busy border crossing had closed on Wednesday after Pakistani and Afghan Taliban forces started firing at each other, according to local officials.

Abdul Basir Zabuli, a spokesman for the Taliban-led police in Afghanistan's eastern Nangarhar province, where the crossing lies, said that authorities from both countries were trying to determine the reason for the clash.

The Torkham border point is the main point of transit for travellers and goods between Pakistan and landlocked Afghanistan.

Ziaul Haq Sarhadi, director of the Pakistan-Afghanistan Joint Chamber of Commerce and Industry, said hundreds of trucks laden with fruit, vegetables and other goods were stuck due to the closure.

"The traders are suffering heavy losses after the border in Torkham was closed on Wednesday following a firing incident there," he told Reuters.

The entire flow of trade had been affected and loading of goods in the southern port of Karachi had been disrupted.

Disputes linked to the 2,600 km (1,615 mile) border have been a bone of contention between the neighbours for decades.

In a separate incident, Pakistan's military said four soldiers had been killed in clashes in Chitral district, near the Afghan border, on Wednesday and that 12 militants had died.