What began as a stroll in the Singapore Botanic Gardens yesterday took a horrific turn when a 40m tembusu heritage tree crashed onto unsuspecting visitors, leaving one Indian national dead and four other people injured, including children.

Mr Jonathan Ang, 29, who was sitting 30m away, described a cracking noise that "sounded like thunder" at about 4.25pm. Just seconds later, the tree hit the ground, bringing down nearby palm trees.

The tree, which was more than 270 years old, landed on a woman from India, pinning her face down. Her husband, a French national, whose head was bleeding after being hit by branches, was heard shouting for his wife.

Other visitors rushed to her aid. "One, two, three push," they shouted as they heaved the tree off her. When it did roll away, Mr Ang saw the victim's limp body and her husband sitting in shock by her side. By then, Singapore Civil Defence Force (SCDF) officers had arrived and the crowd was dispersed.

The site of the crash was about 30m away from the the Shaw Foundation Symphony Stage, where preparations were taking place for a concert to celebrate Canada's 150th anniversary. The crash happened just half an hour before the start of the concert.

Green landmarks

Q What are heritage trees? A They are mature trees that serve as important green landmarks, according to the National Parks Board (NParks), which administers the Heritage Tree Scheme. Before a tree is endorsed as a heritage tree, it has to meet a number of qualifying criteria. This includes having a girth, or trunk circumference, of more than 5m and/or having any botanical, social, historical, cultural and/or aesthetic value. As of Nov 10 last year , there were 266 heritage trees in Singapore. Q What are tembusu trees? A These are large evergreen trees native to Singapore that can grow up to 40m in height. Its trunk has distinctive dark brown fissured bark, and its leaves are light green in colour. The flowers are creamy white, turning yellow with age, and are strongly fragrant especially in the late evenings. Fruits are tiny red berries, that take more than three months to mature. NParks, on its website, says the wood of the tree is extremely durable and resistant to termite attack, making it highly suitable for heavy construction, bridges and carving. The most famous tembusu is the one at Lawn E of Botanic Gardens near the Swan Lake. The tree, which is more than 200 years old, is featured on Singapore's $5 note. It was fenced up in 2013 to prevent visitors from treading around it and affecting the growth of its roots. Yesterday, a different tembusu tree located at the edge of Palm Valley in the Gardens was uprooted.

The police said in a statement: "The police confirm that the deceased was a 38-year-old female Indian national who was there with her family. Her husband, a 39-year-old French national and their two children both aged one... sustained injuries. A 26-year-old female Singaporean was also injured in the incident."

NParks, which manages the Gardens, said: "We are investigating the cause of the tree fall. It was last inspected in September last year and was found to be healthy."

270-YEAR-OLD TREE PREDATED BOTANIC GARDENS A 40m-tall tembusu heritage tree with a girth of 6.5m was uprooted at 4.25pm yesterday at the edge of Palm Valley in the Singapore Botanic Gardens. This tree was more than 270 years old and predated the establishment of the Gardens. It fell and brought down surrounding palm trees. We are investigating the cause of the tree fall. It was last inspected in September last year and was found to be healthy. As a Singapore Botanic Gardens heritage tree, it was inspected twice a year, which is a higher frequency than for other trees in the Gardens. The tree was also protected by a lightning conductor and fenced off to prevent compaction of its root zone by visitors. Leaf litter is routinely applied to the root zone to encourage healthy root growth. We are sad that there was one fatality and four injuries. Our priority now is to accord assistance to the families of the deceased and the injured. NPARKS, in a statement

The tembusu tree predates the establishment of the Gardens, which was founded in 1859, and became Singapore's first World Heritage Site in 2015.

"As an SBG Heritage tree, it was inspected twice a year, which is of a higher frequency than other trees in the Gardens. The tree was also protected by a lightning conductor and fenced off to prevent compaction of its root zone by visitors. Leaf litter is routinely applied to the root zone to encourage healthy root growth," NParks said.

It added that its first priority was to help the families of the victims.

Visitors to the park were left shocked by the incident.

Artist Tina Fung, 34, had produced an art installation that was supposed to have been unveiled at the Canada 150 event yesterday. Describing the aftermath of the tree fall, she said: "Two guys had scratches on their legs, and there was a lady they were trying to resuscitate.

"It looked pretty serious."

Ms Esther Ho, who is in her early 50s and semi-retired, was at the Gardens for the concert. She said: "I am surprised to see a tree with such deep roots fall. I had never heard of this happening before."

Said Mr Ang: "It was so unexpected that a tree with such deep roots could suddenly uproot itself."

Dr Shawn Lum, a botany expert from the Nanyang Technological University's Asian School of the Environment, said a possible, but unlikely, reason for the tree uprooting could be that rot or a fungal infection had occurred in its root area, causing it to weaken.

However, this is not a common occurrence in tembusu trees, said Dr Lum, who is also president of the Nature Society (Singapore).

The recent heavy rains and yesterday's gusty winds could also have been a factor, he said.

The National Environment Agency had forecast that it would be occasionally windy yesterday, with passing showers in the afternoon.

Dr Lum said: "The tembusu that fell is on a slope, although not a very steep one. But after the recent heavy rains and the very gusty winds today and yesterday, it could be that the slope gave way first rather than the tree itself."

What caused the tree to uproot still remains to be seen, said Dr Lum, but it is something that could not have been anticipated.

In a Facebook statement, police advised members of the public to stay away from the site to facilitate rescue work by the Singapore Police Force and the SCDF, which sent two fire engines, one Red Rhino, one Fire Bike, four ambulances and two support vehicles to the scene.

All remaining programmes at the Gardens yesterday were cancelled. But NParks said the Gardens will remain open today.

Deputy Prime Minister Tharman Shanmugaratnam said in a Facebook post last night: "What a terrible accident. Our deepest sympathies to the family of the person who was killed by the falling tembusu tree at the Botanic Gardens this afternoon. Hope the four others injured will recover soon."

•Additional reporting by Felicia Choo and Janice Tai