She had complained about hearing voices in her head over the past week so her friend decided to take her to consult a medium on Tuesday.
Before they set off, Ms Ho Chieu, a 25-year-old Vietnamese who was on holiday here, seemed frightened.
The friend, a 50-year-old Singaporean man who declined to be named, said: "She told me not to leave her alone.
She wouldn't even let me go to the toilet to shower or to change my clothes."
As he was carrying her on his motorcycle on the viaduct of West Coast Highway near VivoCity, she suddenly jumped off.
He said: "I felt my motorcycle shake and immediately braked and turned around.
By that time, she was already at the railings.
"I shouted and pleaded for her not to jump but it was too late. She was gone."
An eyewitness said she saw Ms Ho falling from the viaduct, which is about six storeys high, and a car slamming into her before she landed on Telok Blangah Road.
Ms Ho was pronounced dead at the scene by paramedics, the police said.
The friend said he did not know what to do after Ms Ho jumped, so he got off his bike and made his way down to Telok Blangah Road.
"By the time I got there, the ambulance was there.
I pleaded with the paramedics to save her but it was too late."
He said that he had earlier taken her to a medium near Beach Road but she still complained that she was hearing voices.
So he decided to take her to another medium in Chinatown on Tuesday.
Ms Ho arrived in Singapore last month for a holiday and to visit some of her friends who are living here.
The friend, who had known her for seven years, said she rented a room in an apartment during her stay here.
A student who was waiting for her boyfriend at a bus stop near the Seah Im Food Centre at about 3.15pm, said she saw Ms Ho hurtling down to the road below.
Wanting to be known only as Miss Pamela, 21, she added that a car hit Ms Ho before she landed on the road.
As passers-by screamed and gasped, a motorcyclist skidded and crashed as he tried to avoid hitting the woman.
Miss Pamela told The New Paper in a phone interview yesterday that as the woman struggled to breathe, her blood began flowing onto the road.
She said: "By the time I noticed the woman, she was already in mid-air.
As she was falling, a car hit her before she landed on the road."
Miss Pamela said she was numb with shock and fear.
Some people, including a Caucasian woman, ran across the road to try to help Ms Ho.
"Other passers-by tried to divert traffic away from where the woman was.
"The Caucasian woman stayed by the woman's side throughout," she said.
Some drivers used their cars to shield Ms Ho, who was bleeding profusely, from oncoming vehicles.
Said Miss Pamela: "After the woman landed onto the road, I could see she was still alive as she was struggling to breathe.
"But perhaps her injuries were too serious, because she stopped breathing by the time the police and ambulance arrived," said Miss Pamela.
A police spokesman told TNP that they received a call for assistance at about 3.17pm.
The Singapore Civil Defence Force (SCDF) was informed at the same time and sent an ambulance to the scene, said a spokesman.
When the officers arrived, they found the motionless body of a 25-year-old woman, the police spokesman said.
The police cordoned off one of the five lanes of the east-bound side of Telok Blangah Road for about four hours, reported Shin Min Daily News.
Said Miss Pamela: "It was traumatising and scary.
I can still picture the scene in my head when I close my eyes.
I can only send my condolences to the woman's family."
Ms Ho's father flew to Singapore from Vietnam last night after hearing of her death.
Undertaker Roland Tay is helping Ms Ho's family with funeral and cremation arrangements.
"When I heard about this case from a friend, my heart went out to Ms Ho and her family.
This is a very tragic case as I understand her family is not well-to-do.
I'll do what I can for her and her family," he said.
The police are investigating the unnatural death.
Samaritans of Singapore
Singapore Association for Mental Health
Institute of Mental Health's Mobile Crisis Service
Care Corner Counselling Centre (Mandarin)
This article was first published on Mar 5, 2015.
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