"I just lost it." Mum's warning after 3-year-old suffers horrific treadmill accident.

Warning: The images in this post may be distressing to some readers.

Perth mother Kelly Gay was on the phone last Saturday when she heard a scream from her children’s toy room.

When she went to check on her kids, she found her three-year-old daughter pinned between the wall and the conveyer belt of her treadmill.

Kelly described the injuries little Sienna had sustained “the most horrific sight”.

"I will never get it out of my mind," she told Daily Mail Australia.

"I just lost it and screamed, 'Her hand, her hand!'," Kelly added to 7 News.

Sienna Gay was dragged under the conveyer belt of the treadmill, which was travelling at the maximum speed of 22km per hour at the time, after her brother accidentally turned the exercise machine on.

"Her stomach was all just pink, her hand looked like it had been through a meat grinder," Kelly said of her daughter's injuries.

Sienna was rushed to hospital to undergo a two-hour surgery, where skin was grafted from her bottom to her hand and stomach.

Despite her injuries - which have given little Sienna nightmares and mean she has to wear a compression burns suit for at least two years as she undergoes rehabilitation - Kelly said things could have been "so much worse.

"There's a chance she could've been pulled right under the belt and that would've got from head to toe," she said.

"We're lucky [Sienna's dad] was there and got to her quick enough."

Kelly told Daily Mail Australia her husband had to use "all his strength" to stop the belt of the treadmill in order to free Sienna.

The family will find out on Wednesday whether Sienna requires any further surgery.

Kelly is now offering a warning to other parents to take extra safety precautions with exercise equipment around children.

"Turn it off at the wall, pull the chord out and hide the key," she said.

"Do not leave the key or any exercise equipment around young children. They are curious and intrigued."