Mr Tay Zhi Ming was busy collecting payment at the drinks stall when a sudden movement caught his eye.
The 75-year-old looked up and saw a woman shoving a cleaner in the back.
"I was shocked to see her behaving so violently," Mr Tay told The New Paper.
The cleaner fell forward and hit her head on the corner of a table before collapsing on the floor. The incident happened on Thursday at 9.50am at Bendemeer Market & Food Centre.
Shop owners said the woman, believed to be in her 50s, is a familiar face there. She often goes around collecting cardboard on her cart.
The victim is Ms Liu Li, 42, a cleaner from Sinlik Cleaning Services.
An onlooker who wanted to be known only as Madam Tan said she saw Ms Liu try to get up. She then scratched the woman's cheeks and left upper arm.
The cleaner then fell again and lay motionless on the floor while bystanders tried to help her up.
Singapore Civil Defence Force (SCDF) personnel later arrived and took Ms Liu to the hospital in an ambulance.
Mr Tay also said there was blood on both the floor and the table. He added that it was not the first dispute between the two.
On Wednesday, they had a disagreement over a table stacked with dirty plates. Mr Tay said the woman was upset the table was not cleared and started arguing with Ms Liu. He said she became so agitated that she knocked Ms Liu's glasses off.
Owner of Sinlik Cleaning Services, Mr Chua Hong Cher, 75, said: "I have heard the woman getting into arguments with other shop owners before, but this is the first time it has happened to one of my cleaners."
Vice-chairman of the Bendemeer market committee Lee Kok Wah, 58, added that many shop owners were wary of the woman due to her aggressive temperament.
"She is known to be a troublemaker," he said.
A SCDF spokesman said they received a call at about 9.50am on Thursday, and sent an ambulance to the scene. A woman in her 40s was taken to Tan Tock Seng Hospital and the police are investigating.
This article was first published on September 27, 2014.
Get The New Paper for more stories.