THEY are two of Australia's best-known stars, but Delta Goodrem's homage to Olivia Newton-John failed to impress some viewers.

The 33-year-old singer's performance as the Grease icon in mini-series Olivia: Hopelessly Devoted To You was slammed as "awful" and a "debacle" after it screened last night.

"Olivia must be cringing," one fan wrote on Twitter. "So bad."

Another joked that it made them want to fake their own death and disappear to Mexico, a reference to Newton-John's ex-partner Patrick McDermott, who was thought to have done exactly that after he vanished during a 2005 fishing trip.

"This is a struggle to keep watching," one viewer tweeted, while another observed that "the paint on my wall dried quicker."

Some viewers thought Morgan Griffin, who plays the young Olivia, put in a better performance than Delta, who starred in Home and Away before shifting focus to her singing.

Several people criticised the two-part Channel 7 production, calling it "dodgy" and "cheap", and comparing it to "a dramatic reading of Olivia Newton John's Wikipedia page."

But a few gave the show positive reviews, revelling in the carefully recreated outfits and locations. One viewer said people had expected the biopic to be a trainwreck but it was, in fact, "quite good".

And The Voice coach did have her fans, with some saying, "No one could have done it better" and calling her "out of this world".

She said she probably wouldn't watch it, but accepted that it was going to happen whether she liked it or not, and wanted to see Delta star in it.

She eventually agreed to record two songs for the soundtrack, I Honestly Love You, with Delta in Los Angeles.

The two women are friends, with Newton-John becoming a mentor to the Born To Trysinger after they met in New York when Delta was a starstruck seven-year-old.

There are many parallels between their lives and careers, with both writing hit albums as well as acting and fighting cancer. Newton-John, who had breast cancer, contacted Delta when she was diagnosed with Hogkins Lymphoma at 18.

Newton-John's cancer battle, her stalker and her split from ex-husband Matt Lattanzi, played by Richard Brancatisan, are among the challenging moments portrayed in the two-part series.

Part Two of Olivia Newton-John: Hopelessly Devoted To You airs on May 20 at 8.30pm on Seven.