A man who is under police guard in Royal Perth Hospital has had a bedside court hearing, accused of setting his girlfriend on fire in Perth's southern suburbs.

The woman in her 20s ran ablaze from a Tay Court house in Gosnells to a nearby park yesterday afternoon where witnesses poured water on her to douse the flames.

She remains in a serious condition in Royal Perth Hospital with burns to the upper part of her body.

Johnathan Pauu, 22, who is also suffering from burns, has been charged with acting with intent to cause grievous bodily harm.

He has been remanded in custody to appear in court next week.

Yesterday, a neighbour Tristan said he ran to see what was going on.

"Yeah [she] was just running through the park with all clothing on fire and pretty much got to the end of the park and turned the corner," he said.

"There was the big guy pouring water on someone and another guy pouring water and we looked and it was the chick and she was burnt pretty much from the waist to the top of her head."