Shoppers have been left shaken after part of a roof caved in during peak Christmas trade.

Panic erupted as rubble fell from the second storey at a Lidcombe shopping centre in the heart of Sydney, forcing crowds to scramble for safety.

WATCH THE VIDEO ABOVE: Shopping centre roof collapses in the middle of Sydney

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The centre has been partially shut while investigators work to determine the cause.

One person is being treated by paramedics at the scene.

Fire Rescue NSW Inspector Steve Brown said crews were first alerted at 1.50pm when an automatic fire alarm was triggered inside the Parramatta Road complex.

“Almost immediately after that activation, triple zero calls began reporting a ceiling collapse and injuries,” Brown said.

A roof has collapsed at Lidcombe shopping centre. Credit: Gatot Sydney

Two fire trucks and eight firefighters were initially dispatched, but the response quickly escalated to five trucks and 20 firefighters, including specialist rescue crews.

Authorities say the collapse may have been linked to a sprinkler head activating in the ceiling space, though the exact cause remains unclear.

Significant flooding has been reported inside the centre.

Firefighters are working to shut off the water supply and begin the clean-up.