"It appears at this early stage the woman, believed to be aged in her 20s, may have walked on and entered the track to try to retrieve a dropped phone before she was hit by a rollercoaster carriage, about 5.45pm.
"Sadly the woman was then found injured on the ground. Detectives from the Yarra Crime Investigation Unit are attending the scene and will work with WorkSafe to establish the circumstances surrounding the incident."
The Melbourne Royal Show released a statement confirming there had been a "reported injury on the Rebel Coaster ride".
"We are working closely with the ride operator, WorkSafe Victoria and Victoria Police to investigate the issue further. However, we can confirm that no one has fallen from the ride," the event said.
"The ride in question will be closed for the foreseeable future and updates will be made as information comes to hand."
A stall owner at the show told the Herald Sun she heard the rollercoaster stop abruptly as people screamed.
"The screaming was so loud. I think everyone must have been really scared," she said.
"The ride went up like normal, then there were screams, then it stopped and stayed that way for ages."
Those on the ride when it stopped remained stuck there for more than an hour.
