Australian singer Olivia Newton-John has married American millionaire and Amazon herb entrepreneur John Easterling in a surprise wedding on the weekend, according to reports.

The UK's Daily Mail reported Newton-John, 59, and Easterling, 49, told friends and family they were holding a Fourth of July barbecue at her Malibu home.

When the guests arrived, a ceremony took place.

Tragedy has followed the highs of Newton-John's music and film career, with the singer diagnosed with breast cancer in 1992, divorcing first husband Matt Lattanzi in 1995 and dealing with the trauma of the disappearance of her boyfriend Patrick McDermott during a fishing expedition off Los Angeles in 2005.

Drama almost ended the weekend's wedding, according to the Daily Mail.

A bushfire threatened Newton-John's multi-million dollar Malibu home before the ceremony.

"John said they could wait a few days, or change the venue, but Olivia was determined that nothing was going to interfere with her special day," a source told the UK newspaper.

Newton-John, who has daughter Chloe, 22, with Lattanzi, and Easterling have been together for over a year.

They appeared together at a public event for the first time in January at the G'Day USA Ball in Hollywood where they held hands on the red carpet and snuggled together inside.

Newton-John performed some of her Grease hits at the ball for the 1,000-plus audience that included her Grease co-star John Travolta, who opted not to sing.

Easterling is the founder and chief executive of the Amazon Herb Company.