After his lunch, the gardener was walking to throw away the packet when an excavator hit him and pierced his left thigh.
Mr Lee Wei Kee's colleagues at Prince's Landscape and Construction, who witnessed the accident on Thursday, said they "saw his thigh get pierced before he screamed and fell to the ground", Chinese evening daily Lianhe Wanbao reported.
It is understood that a major artery was severed, causing Mr Lee, 29, to bleed profusely.
The Singapore Civil Defence Force (SCDF) said it was alerted to the incident at about 1.25pm.
An ambulance took the victim, who had sustained injuries to his left leg, from 52, Sungei Tengah Road, to National University Hospital, its spokesman added.
The New Paper understands that Mr Lee died on the way to the hospital.
The police said that a 30-year-old man was arrested for causing death by a negligent act and investigations are ongoing.
When The New Paper visited the nursery yesterday, a spokesman for Prince's Landscape and Construction declined to comment as it was "waiting for police to conclude their investigations".
On its website, the company says that it is one of the oldest nurseries in Singapore, with 50 years of experience in the industry.
From humble beginnings as a flower shop, "Prince's has evolved into a full-fledge landscape design and installation specialist".
At a neighbouring nursery, workers who requested anonymity said they had seen the police and an ambulance heading to Prince's on Thursday.
But they did not go over to find out what had happened and found out about the accident from media reports.
They told TNP that they had never spoken to Mr Lee but often saw him walking to and from work.
They added that "he looked like a jovial person".
Mr Lee's family was at the mortuary yesterday morning to identify his body and make funeral arrangements.
His uncle, a 53-year-old security guard, told Lianhe Wanbao and Shin Min Daily News that his nephew was autistic and got the gardening job about five years ago after a social worker helped to arrange employment for him.
Giving his name as Mr Wong, he added that Mr Lee would go to work every day from 8am to 5pm, and then head to church before heading home by 10pm.
"He is usually an obedient person and will get angry only when provoked," Mr Wong said. "He has no hobbies, spends no money and gives his monthly salary to his mother as he is a filial son."
He said that Mr Lee's mother, who became a widow three years ago, was distraught over the tragedy.
Mr Lee's brother was on a flight from Hong Kong, where he was on a business trip, he added.
A Facebook post reveals that Mr Lee was popular among the congregation at City Harvest Church, where he was fondly known as "Superman".
"He was tall, strong and fast on his feet so some folks gave him the name 'Superman' and I guess it just stuck," said Mr Shane Chiang, 43, who attends the same church.
"He was the man that most people knew because he loved going to church and attended services all the time," he added.
Mr Chiang said he fondly remembers Mr Lee for his perseverance, especially when trying to cope with his autism.
"It was hard for him to sit down and listen (due to his autism) but I remember seeing him really try."
This article was first published on August 1, 2015.
Get The New Paper for more stories.