Diesel was no longer on sale across Sri Lanka on Thursday, crippling transport as the crisis-hit country's 22 million people endure record-.
The South Asian nation is in the grips of its worst economic downturn since independence, sparked by an acute lack of foreign currency to pay for even the most essential imports.
Petrol was on sale but in short supply, forcing motorists to abandon their cars in long queues.
"We are siphoning off fuel from buses that are in the garage for repairs and using that diesel to operate serviceable vehicles," Transport Minister Dilum Amunugama said.
Owners of private buses -- which account for two-thirds of the country's fleet -- said they were already out of oil and that even skeleton services may not be possible after Friday.
"We are still using old stocks of diesel, but if we don't get supplies by this evening, we will not be able to operate," chairman of the private bus operators association Gemunu Wijeratne told AFP.
The state electricity monopoly said they would be forced to enforce a 13-hour power cut from Thursday -- the longest ever -- because they did not have diesel for generators.
He said hydro reservoirs, which provide more than a third of electricity demand, were also dangerously low.
The lengthy power cuts forced the Colombo Stock Exchange to limit its trading by half to two hours, while many offices asked non-essential staff to stay at home.
The electricity rationing also hit mobile phone base stations and affected the quality of calls, operators said, adding that their stand-by generators were also without diesel.
The shortages have sparked outrage across Sri Lanka, with local television reporting protests across the country as hundreds of motorists block main roads in several towns.
Several state-run hospitals have stopped surgeries as they have run out of essential life-saving medicines, while most have stopped diagnostic tests which require imported chemicals that are in short supply.
Colombo imposed a broad import ban in March 2020 in a bid to save foreign currency needed to service its $51 billion in foreign debt.
But this has led to widespread shortages of essential goods and sharp price rises.
The government has said it is seeking a bailout from the International Monetary Fund while asking for more loans from India and China.
Sri Lanka's predicament was exacerbated by the Covid-19 pandemic, which torpedoed tourism and remittances.
Many economists also blame government mismanagement including tax cuts and years of budget deficits.