SINGAPORE , June 16 — Office workers near a Tanjong Pagar building site where an estimated 50-tonne concrete wall collapsed and killed a worker yesterday described hearing an "extraordinarily loud” crash and experiencing tremors when the incident happened, leaving some of them stunned.

One of them, who wanted to be identified only as Nikolas, was at his office on the 11th floor of ABI Plaza, about 50m away from the site, when the collapse happened.

The 39-year-old who works in oil and gas projects told TODAY that he heard a loud boom that "sounded like something big was collapsing” and felt mild tremors at about 2pm.

Initially, he and his colleagues did not think much of it, thinking it was normal demolition work going on at the former Fuji Xerox Towers on Bernam Street to make way for a mix-use development.

"There are many construction sites in this area and they are always drilling. So we thought the loud noise and the vibrations in the ground were just part of the demolition project going on.”

They were shocked at the sight of the collapse when they took a look out onto the street.

"We could see everything from the 11th floor and it was really bad. The whole thing was a mess and we couldn’t recognise the pathway that was destroyed,” he said.

Suren Segaran, who is a director of a company located near Bernam Street, said that the reinforced concrete wall collapsed onto a footpath that he usually uses.

The 35-year-old said: "I walk along that pathway quite often as it’s located between my office and the place where I usually get lunch. I’m just glad that I didn’t walk there today when the structure collapsed, which was just past an hour after lunch time.”

The Ministry of Manpower (MOM) and Building and Construction Authority (BCA) said in a joint statement on last night that a reinforced concrete wall on the second storey, measuring about 10m long and 3.8m high, had collapsed onto Bernam Street as it was being demolished.

The Singapore Civil Defence Force (SCDF) said in a Facebook update at 10.15pm that a worker who had been reported missing earlier was first sighted pinned under the collapsed structure at around 6pm.

"The worker had no pulse and was not breathing,” it said, adding that the worker was pronounced dead after a nearly four-hour operation to free his body.

MOM and BCA said the worker was an Indian national and that they had stopped all work at the site and are investigating the incident. SCDF said the worker was 20 years old and that it was alerted to the incident at Bernam Street at around 2pm.

When TODAY arrived at the scene at about 4.30pm, the authorities had cordoned off the entire Bernam Street, a one-way street of about 150m connecting Tanjong Pagar Road with Anson Road.

The cordon and the presence of various SCDF and police vehicles around the area, meant the view of the actual site where the concrete slab had collapsed was limited.

Still, that did not stop curious passers-by — most of whom were office workers in the area — from stopping in their tracks and observing the search operation at work.

TODAY managed to get a view of what was happening inside the sealed area from the seventh floor of the multi-storey carpark of M Hotel, which overlooks Bernam Street.

SCDF officers could be seen using heavy plant machinery and other rescue equipment to try to free the trapped construction worker from underneath the concrete slab.

The collapsed concrete wall’s weight also appeared to have pulled down a scaffolding structure, leaving it in a mangled rubble.

Workers nearby felt tremors, thought it was an earthquake

TODAY spoke to five workers whose offices were near the scene of the incident.

One of them, who wanted to be known only as Amanda, said she was immersed in her work after lunch hour at her office in the Anson House building located right across the construction site, when the concrete wall collapsed.

The impact of the collapse was strong enough to send shockwaves through the ground, which she and her colleagues felt while working on the fourth floor of the building.

"We heard a loud ‘thump’ sound which happened very quickly. But what jolted us was the feeling of the building moving and shaking,” said the woman in her 20s.

The office was used to loud noises and slight vibrations coming from two nearby construction sites, she added.

"But this one was exceptionally loud (and) on another level. Everyone, no matter what they were doing, were stunned and looked up from their work,” she said.

"My chief executive officer who’s usually cooped up in his office attending video call meetings was very startled and even came out of his office to see what was happening.”

Another employee who gave her name only as Lee similarly said that she felt the ground shaking on the fourth floor of Anson House at the time of the structure collapse.

"My colleagues and I were so surprised when it happened. We felt the ground shake, along with a loud noise as if something was falling,” said the 26-year-old, who works in advertising.

"The loud noise was also different from the usual construction noises we are used to hearing in this area. Then one of my colleagues showed us the news.”

Avinishea Rupadas, manager of restaurant Napolizz Pizza which is located at the first level of Anson House, said that she did not feel the tremor but heard a loud crash.

"It sounded different from the typical loud construction noises, so I went out to see what was going on. I saw a thick, grey cloud of dust in the air where the crash happened.”

By the time she saw the scene, a small crowd of nearby office workers had formed near the worksite.

"Some of the office workers came down because they saw the crash from above, or because they felt tremors on the ground,” the 29-year-old manager said. — TODAY