Witnesses told the High Court in Glasgow how they tried to stop the bleeding as Javaid Ali lay at the back of his store in Green Road, Paisley, on June 15 last year.
They were giving evidence at the trial of Lee Anderson, who denies murdering 48-year-old Mr Ali by stabbing him in the neck and wrist with a knife at the Sunshine Licensed Grocers.
Eileen Meechan sobbed as she told prosecutor John Scullion blood was coming out of Mr Ali's neck like a fountain.
Grandmother Ms Meechan, 48, said when she walked into the shop there was nothing untoward and no signs of any disturbance.
She told the jury Mr Ali was at the back of the store on his phone and staring at her. Ms Meechan told the court she jokingly asked him go get off the phone and come and serve her.
Seconds later he collapsed. At first she said she thought he was kidding her on. But then she saw blood coming from his neck.
Ms Meechan said: "I noticed the blood was coming out of his neck like a fountain. I ran out the shop and then ran back in and phoned an ambulance."
The court also heard from 999 operator Spencer Anderson, who took a separate call from Mr Ali at 5.07pm. Spencer Anderson said: "He said he had been stabbed in the neck and was bleeding badly."
The operator said the call cut off and he tried unsuccessfully three times to call Mr Ali back.
In her evidence, Ms Meechan described Mr Ali as an outgoing character who always chatted to his customers. She said he also loaned money to them and had told her he was owed £1000 by one person.
Defence QC Brian McConnachie put it to Ms Meechan: "After this incident in 2012, Paisley and the area round Green Road was rife with rumours about who had committed this crime" She replied: "Yes."
Mr McConnachie then said: "One of the names that cropped up in these rumours was your son." She replied: "Yes."
Another regular customer, Joanne Haveron, 52, a cleaner who came into the shop minutes after Ms Meechan, said she put a nappy on Mr Ali's neck to stem bleeding.
Ms Haveron said she then left the shop to find help. She wept as she said: "I was scared, shocked and upset. I've never dealt with anything like that before."
The court heard she asked a man walking along Green Road to help and he went into the shop and applied pressure to the wound with the nappy until paramedics arrived.
Alan Nimmo, 34, from Paisley, said he tried to comfort Mr Ali as he lay bleeding. Mr Nimmo said Mr Ali was sitting slumped in the back area of the shop.
He added: "At first I thought he looked alright, then I looked again and I thought 'oh no' when I saw the hole in the side of his neck."
Mr Nimmo said Mr Ali made a gurgling noise. "I said: 'Who done this to you Jav? You're going to make it'," Mr Nimmo added.
Mr Nimmo, a regular customer at the Sunshine Grocers, told the court that in the two months before Mr Ali was stabbed, he was selling cannabis to some of his customers, including himself.
Paramedic John McManus, 52, told the jury he and his colleagues battled to save Mr Ali's life after he went into cardiac arrest.
He was given CPR all the way to the hospital but died from his injuries on June 29 last year.
Lee Anderson is also accused of attempting to pervert the course of justice and carrying a knife. He denies all charges against him.
The trial continues.