A Christmas balloon drop in Sydney's Westfield at Parramatta has descended into chaos overnight with five people taken to hospital after being crushed.

Police say a number of people were knocked over and injured when the crowd surged as prize-filled balloons were released during the shopping centre's "mega balloon drop".

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"They were at that location to grab balloons as they were released and apparently the balloons had small gifts inside," a NSW Police spokeswoman told AAP on Tuesday.

Paramedics treated 12 shoppers at the scene and five people were taken to hospital, according to NSW Ambulance.

Inspector Phil Templeman said they were responding to reports that the balloon drop "caused a stamped of people to hustle for the prizes".

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"Three of the transported patients had more serious issues including traumatic chest injuries, neck and back pain as well as nausea and dizziness," Insp Templeman said in a statement on Tuesday.

He said it was "incredibly lucky" that no one was more seriously injured.

"As we go into the busy holiday period and many of our shopping centres become crowded with people, we urged the community to be patient and ensure the safety of themselves and those around them," he said.

Westfield had been promoting the balloon drop as part of a 33-hour non-stop shop.

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In a statement, Scentre Group, owner of Westfield shopping centres in Australia, said that the circumstances around the incident were being investigated.

"The safety of our customers, retail partners and people is our priority," it said.

"Our team acted swiftly to support our customers, contact emergency services and make the area safe. Our team are continuing to speak with affected customers directly."

Meanwhile, if you're brave enough to have left your Christmas shopping to the last minute, you still have some time to get your hands on a gift.

Westfield in Sydney's Parramatta will be open until 6PM on Tuesday, the same for Melbourne's Chadstone shopping centre.

Adelaide's Marion Westfield is also open until 5.30PM while Perth's Carillion City shopping centre is open until 9PM.

- With AAP