The smoke in the workshop caught their attention.
Workers at Eu Guan Machinery, a lorry scrapyard in Sungei Kadut Avenue, quickly grabbed extinguishers to try to fight the fire.
But in less than 10 minutes, the situation had spiralled out of control and they fled in the opposite direction.
The blaze, which happened on wednesday afternoon, damaged part of the company's workshop.
A witness, Mr Ayakanu Sundram, 39 said: "We heard small explosions and we came out of our workshops to have a look.
"By then, there was a huge fire and we saw workers running away."
Mr Sundram, a welder, decided to flee with his colleagues.
Mr Mohd Rahman Shah, a clerk from Eu Guan Machinery, said the fire started at about 3pm. He suspects that it originated from a pile of lorry tyres behind the workshop.
He said: "The workers tried to douse the fire using fire extinguishers. But the flames didn't die off. In fact, it got worse."
The fire spread quickly, even reaching the workshop's 30m-high ceiling.
The intensity of the fire caused some of the inflated tyres to explode.
"That's when the call was made to evacuate our 12 workers," said Mr Mohd. "We knew there was nothing we could do other than call the authorities."
The loud "pop" sound could also be heard 300m away, at an executive condominium in Yew Tee.
The New Paper (TNP) received a call about the fire from a man who wanted to be known only as Jon.
His daughter saw the fire from the family's eighth-floor unit.
Said Jon, who sent TNP a video of the fire: "Black smoke from the workshop blaze rose to a height as tall as my condo unit. It was quite spectacular."
While some workers had dashed to safety, others - like several from the workshop next door - decided to stay to watch the unfolding drama.
A worker from India, who gave his name only as Mr Ramesh, said: "It was our tea time. We could tell that it was not a gas explosion, so it was safe to watch."
Mr Ramesh and some of his colleagues from a concrete pre-fabrication company 50m away.
As a precaution, he switched off the power for the tools used by workers at his company.
The Singapore Civil Defence Force (SCDF) said preliminary investigations showed the fire may have started near a pile of wooden items and tyres.
SCDF spokesman said the fire was within a 6m by 7m area and had spread to the ceiling. The fire was extinguished within five minutes.
Looking at the smouldering remains of the tyres, Mr Mohd said: "Luckily, nobody was hurt. The next step for us is to figure the company's loss in the fire.
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