Rumer Willis is "handling" her mother's problems well, says Zac Efron.

Zac and Rumer have been romantically linked in the past, but it's thought they are just close friends.

Rumer's mother Demi Moore is going through a hard time at the moment after being hospitalised following a seizure at home last month. There were reports she needed help for anorexia and substance abuse issues and she is now thought to be receiving treatment at Cirque Lodge rehab centre in Utah.

Zac has been in touch with Rumer and has let people know she is coping well.

"She's doing OK, she's doing fine. It's tough what she's going through right now, but she seems to be handling it really well," he told Access Hollywood.

Zac was speaking while promoting his new animated movie Dr. Seuss' The Lorax.

He voices the character of 12-year-old Ted, who is trying to win the affections of Audrey. Taylor Swift lends her vocals to Audrey and Zac admits struggling with some aspects of the picture.

"I had just finished filming [The] Lucky One, I was 15lbs. heavier. Then I had to come in and do these voices and he was 12," he laughed.

The 24-year-old found a special diet helped him get into character, and he also pictured an actor who reminded him of Ted.

"I was early in the morning drinking green tea, trying to get my voice up high as high as humanly possible," Zac explained.

"He's a real spontaneous, fun loving guy, but I sort of pictured him like Michael J. Fox. He's really high energy."