Olivia Newton-John remembered by John Travolta: 'Love you so much'

John Travolta has led the tributes to Dame Olivia Newton-John, who died in Southern California aged 73 on Monday morning (local time) after a battle with breast cancer.

Travolta wrote an emotional post on Instagram, addressed to "my dearest Olivia".

"You made all of our lives so much better. Your impact was incredible. I love you so much.

"We will see you down the road and we will all be together again.

"Yours from the first moment I saw you and forever! Your Danny, your John!"

READ MORE: Olivia Newton-John dies after battle with breast cancer, aged 73

The pair starred alongside each other in the 1978 musical film Grease, singing major duets You're the One That I Want and Summer Nights. The film's soundtrack is one of the best-selling movie soundtracks of all time.

The British-born, Australian-raised singer and actress was a four-time Grammy Award winner and also campaigned extensively for environmental and animal rights issues.

American singer and actress Barbra Streisand wrote that her friend was "too young to leave this world".

"We have lost a great, iconic artist in Olivia Newton John, gone too soon from us at age 73," said John Takei.

"I trust she is now in the great Xanadu beyond. Know that we are forever hopelessly devoted to you, Olivia. Rest in song and mirth."

Long-time friend Richard Marx said his heart was broken.

"Rest now, sweet friend. You were as kind and loving a person as there’s ever been. I’ll miss you every day."