The explosion that rocked a shopping centre in Haymarket in Sydney’s CBD could have been much worse if not for the quick thinking of one of the security guards, shop owners say.

Security guard Khalifa Azrag was called to the basement of the Dixon House shopping centre by a cleaner when he smelt gas just before 7.40 pm on Tuesday.

“There was gas leaking in the basement near the pump room,” said Mr Azrag, as he handed out coffee to distressed owners who had come to see the damage to their shops on Wednesday morning.

“The cleaner was inside and smelt gas leaking, and straight away I said it smelt really bad. I came down and shut down the valve, right next to the food court.

“I was on the phone to centre management to find out where the main power was,” he said.

“I just put the phone down and boom.”

The explosion blew out a roller door and sent debris flying, leaving 16 people injured, including a child and a 19-month-old baby.

“Boom, it blow like a bomb, you know,” said Steve Lau, who has owned the Phnom Penh takeaway stall in the Dixon House food court for 21 years.

Mr Lau told customers to “run, run, run,” but was relieved when saw only white smoke and no flame.

“Then I smell the gas smell, not big problem,” he said. “If you got a big problem you got a fire.”

Mr Lau said the fact that Mr Azrag shut down the valve had prevented the initial explosion from completely blowing out the food court, where he estimated 80 people were eating during the dinner rush.

“The kitchens, they are all through the food court. If the flame goes there, it is going to be much worse,” he said.

Superintendent Paul Johnstone from Fire and Rescue NSW said there was no spread of fire after the explosion.

“The sprinklers activated and contained any fire,” he said.

On Thursday, Mr Lau and 20 other owners gathered around Dixon House looking for answers.

The shopping centre that houses the food court remained sealed off by hazard tape, while tourists filed by other undamaged restaurants as they set up for yum cha in the popular street.

“I have nothing: my wallet is inside, the keys inside, no driver licence,” said Mr Lau. “Everything is inside. When you close, you lose the business, you lose the salary.”

More than 200 people were evacuated from the five-storey building that rises up above the food court, which includes grocery stores, a mail service, a doctors’ surgery and hair salons.

Frustrated customers arrived on Wednesday to find businesses remained shut pending the outcome of an investigation.

NSW Fire and Rescue has not advised when the centre will be able to reopen.

Three adults remain at the Royal Prince Alfred Hospital in a stable condition while a child has been treated at the Sydney Children’s Hospital for a lacerations.

There was no damage to surrounding buildings, and the blast is not believed to be suspicious.