Three young women working as promotional staff for a snack food company feared for their lives after their ferris wheel carriage door snapped off metres above Sydney's Circular Quay.

The women were screaming and one had her hand crushed in the amusement ride mishap about an hour after the wheel started turning at the Overseas Passenger Terminal on Monday.

The ferris wheel was stopped soon after the carriage door broke off.

Mother Angie Kelly said her daughter, 24, had been in the carriage with two friends near the top of the ferris wheel when it became unstable and two of the women lurched onto their friend opposite.

Ms Kelly said two of the three women - who did not want to be named - were screaming and one of them had said "We're going to die".