SINGAPORE - Visitors to the Singapore Botanic Gardens on Sunday (Feb 12) morning carried on their activities as usual, a day after a 40m-tall tembusu tree crashed onto unsuspecting visitors, leaving one woman dead and four injured.

Some visitors did their morning strolls or walked their dogs, while others took time to have a picnic or enjoy the surrounding scenery.

Many visitors, including curious tourists, took photos of the fallen heritage tree around the incident site, which remains cordoned off.

When The Straits Times visited early Sunday morning, workers were still trying to remove the fallen tree, which had brought down nearby palm trees when it hit the ground.

Some workers were seen sweeping up tree debris and moving them to the side of the crash, about 30m away from the Shaw Foundation Symphony Stage.

Visitors to the park were surprised to see that the huge tree had fallen to the ground.

Marketing manager Daniel Yeo, 40, who was taking a morning stroll with his wife, said: "I am shocked that a large tree with deep roots could fall."

Despite the incident, he added that they will still frequent the park regularly. "We will be careful to avoid the unsafe areas," he said. "However, more regular checks have to be done, because there are many families with young kids who come here often."

The fallen tree, which was more than 270 years old, landed on a 38-year-old female Indian national, pinning her face down.

She was there with her family on Saturday afternoon when the incident happened. 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 it is investigating the reason the tree fell.

The tree was last inspected in September last year and was found to be healthy, NParks added.

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.

All remaining programmes at the Gardens on Saturday were cancelled. But NParks said the Gardens will remain open on Sunday.

In a statement to the media, the High Commission of Canada in Singapore, which was supposed to hold its event near the site of the crash on Saturday, said it was "deeply saddened by the tragic accident".

"We wish to extend our sincere, heartfelt sympathies to the families and friends of the deceased and to those injured. Our thoughts are with them at this difficult time," the statement added.

"We would also like to express our profound gratitude to those that came so quickly to the aid of others following the accident."

Mr Julien Tan, who is self-employed, was at the Gardens with his family on Sunday.

"It looked quite serious," the 42-year-old said. "I hope those injured will recover from this incident, especially the two young kids, who have lost their mother."

Singaporean plant expert Jean Yong, an eco-physiologist at the Australian Research Centre for Mine Site Restoration, said that the root system of a tree that size could spread over 50m to 100m.

The centre works on research projects underpinning successful mining restoration outcomes. Trees are a key component of ensuring such sites can be rehabilitated.

"Issues relating to urban trees are challenging and require good scientific allometric assessment to better predict tree stability when the soils are very wet, and when encountering a seasonal microbursts of strong gale-force winds," Dr Yong said.

He suggested NParks consider adding in tree specific allometric assessment to better predict changes in tree growth, as roots and stems would have developed separately over the years.

Allometry is the study of the relationship between factors such as size and shape.

Besides tree health, which routine inspections now focus on, constraints to root space volume should also be recognised and documented, he said.

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