A major Sydney shopping centre remains unstable and is in danger of collapsing further in a "domino effect" that could send debris flying hundreds of metres.
Retailers have been kept out of the building in Sydney's southeast, and surrounding roads remained closed on Tuesday evening after the collapse of a nine-metre steel pole that supported the carpark roof.
Emergency services were called to Westfield Eastgardens, in Pagewood, at 7am and 500 to 600 people were evacuated from the shopping centre in Sydney's south. Nobody was hurt.
Police said the collapse could have been disastrous if it had happened just a few hours later when shops were open.
Firefighters are worried that the entire building could collapse if the concrete panels above the shops move, creating a domino effect.
On Tuesday afternoon, Botany Bay Local Area Commander Superintendent Karen McCarthy said the carpark was still unstable.
"It currently still has movement in relation to rubble ... still falling into the carpark," she told Fairfax Radio Network.
"From the eastern and southern sides is where the building is likely to collapse if it does.
Debris could fly for several hundred metres if the building collapsed, she said.
Supt McCarthy said it was unclear how long the shopping centre would remain closed.
Structural engineers, fire and rescue teams and urban search and rescue crews have remained at the scene, and retailers have been told not to enter the building until further notice.
Westfield said in a statement that structural assessment was under way and it was working with authorities to ensure the centre was safe to resume trade.
Earlier, Fire and Rescue NSW told AAP a second-level steel beam that supported the carpark roofing had collapsed.
Former NSW Premier Kristina Keneally provided commentary on the collapse via Twitter soon after it occurred.
"I'm at Westfield Eastgardens. Part of the centre has just collapsed. All inside being evacuated," she wrote on the micro blogging site.
"Lots of fire trucks. Near food court."
Police are contacting the owners of vehicles stuck in the car park, saying they will be able to begin collecting their cars from 7am on Wednesday.
It's good news for all but four owners, whose cars are too close to the safety props to be removed.
A 13-hour emergency services operation to install numerous safety props in the partially collapsed car park ended just after 9pm on Tuesday.
Engineers have stabilised the structure and owners Westfield will continue working on the car park throughout Tuesday night.
Westfield Eastgardens will reopen its doors at 7am (AEST) on Wednesday, after engineers deemed the building was safe to enter.
The food court, which was affected by the collapse in the car park, will remain closed indefinitely while power supplies are restored.
