A Christmas retail shopping marathon has ended in tears and "traumatic" injuries, with several people hospitalised after a giveaway led to a crowd crush at a Westfield shopping centre in Sydney.

As part of its 33-hour shopping marathon on Monday, Westfield Parramatta released balloons filled with gift cards and other prizes at midnight.

In the "stampede" to grab a balloon, participants toppled a makeshift barrier and fell on each other.

NSW Ambulance Inspector Phil Templeman said paramedics treated 12 people after the balloon drop "caused a stampede of people to hustle for the prizes".