A 26-year-old woman is fighting for life after she was hit by a roller coaster at the Melbourne Royal Show and carried nine metres into the air before falling back to the ground.

It is believed Shylah Rodden was retrieving her phone from the tracks of the Rebel Coaster ride when she was hit by the roller coaster about 5.45pm yesterday, after having dropped the phone when she was on the ride.

After the roller coaster struck the 26-year-old, it carried her nine metres up into the air before she fell back to the ground in front of crowds of people.

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She is still in a critical condition at the Royal Melbourne Hospital on Monday evening, while the ride has remained closed today as Victoria Police and WorkSafe investigate the incident.

A witness of the incident has told 9News he watched her fall to the ground after she was dragged up by the roller coaster.

"The carriage had just come to an abrupt stop at the top. I have seen the person fall just straightforward and down," he said.

The man said he had trouble sleeping after seeing the incident.

"You keep picturing it. Trying to figure out what happened and how it's happened and why."

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Another witness has told how "everyone went into shock" after Rodden fell.

"It was silent. Nobody was moving. Nobody knew what to do."

It is thought the roller coaster was likely travelling at a fast pace when Rodden was hit.

The roller coaster is believed to reach speeds of 70km/h.

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Speaking to 9News, Melbourne Royal Show CEO Brad Jenkins has described the incident as a "tragedy".

But he said he was "very confident" that the necessary safe protocols had been in place at the show.

"The protocols and the assessment of the ride, which is done by WorkSafe, are the tightest in Australia," Jenkins said.

Police spent the evening speaking to the many witnesses to the incident, with screams heard after it happened.

People who were on the ride at the time of the incident had to stay on the roller-coaster for hours.

It was initially believed Rodden may have fallen from the roller coaster while riding as a passenger, but the Melbourne Royal Show quickly confirmed that was not the case.

The annual Melbourne event only just returned to the city this week after a two-year hiatus due to COVID-19.