Motorists queue to buy fuel at the Ceylon Petroleum Corporation fuel station in Colombo. AFP

Troops fired in Visuvamadu, 365 kilometres (228 miles) north of Colombo, on Saturday night as their guard point was pelted with stones, army spokesman Nilantha Premaratne said.

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"A group of 20 to 30 people pelted stones and damaged an army truck," Premaratne told AFP.

Police said four civilians and three soldiers were wounded when the army opened fire for the first time to quell unrest linked to the worsening economic crisis.

As the pump ran out of petrol, motorists began to protest and the situation escalated into a clash with troops, police said.

People queue up to buy kerosene for domestic use at a supply station in Colombo. AFP

Sri Lanka is suffering its worst economic crisis since independence, with the country unable to find dollars to import essentials, including food, fuel and medicines.

The nation's 22 million population has been enduring acute shortages and long queues for scarce supplies while President Gotabaya Rajapaksa has for months resisted calls to step down over mismanagement.

Sri Lanka has deployed armed police and troops to guard fuel stations.

A motorist was shot dead by police in April at the central town of Rambukkana when a clash erupted over the distribution of rationed petrol and diesel.

Police said clashes involving motorists erupted at three locations over the weekend. At least six constables were wounded in one clash while seven motorists were arrested.

Agence France-Presse