The 'Downton Abbey' star, who plays the title role in Kenneth Branagh's new big screen adaptation of the fairytale, was taking a break during filming at Pinewood Studios in England when her ballgown was ignited by a portable heater in her dressing room, reported Contactmusic.
The fire was put out and James, 24, escaped without injury.
"It had turned really cold and someone had put a three-bar heater a bit too close to where Lily was going to sit on a stool. Luckily, just a segment of the silk dress got burnt. Thank God Lily wasn't harmed," costume designer Sandy Powell said.