The US star initially postponed one date last week "with great frustration" but battled through a performance on Saturday night.

She was subsequently admitted to hospital in Sydney twice, according to promoter Live Nation.

Monday's concert was called off as fans began to arrive at the venue, while Tuesday's show was also postponed.

"Pink will remain in hospital overnight, continuing her treatment and recovery," said a tweet from Live Nation.

The star, whose real name is Alecia Moore, will be reassessed by doctors on Tuesday.

Her next scheduled concert is on Thursday and tickets are still on sale via Live Nation's website.

The promoter has not indicated whether further cancellations are likely, but said "a further announcement will be made when an update becomes available".

The 38-year-old has been fighting sickness on and off during her marathon Australian tour, which began last month.

Shortly before arriving in Sydney last week, she tweeted fans to ask: "Does anyone have a favourite place that makes wellness shots and fresh juices for when I get there?"

After postponing Friday's concert on medical advice she was pictured on the beach with her husband Carey Hart and children Willow and Jameson, prompting criticism from Australia's tabloid press.

Pink later took to Instagram to defend herself, saying: "What these parasite paparazzi don't show you, is two doctor visits in Byron [Bay] on two consecutive days, antibiotics, steroids, Vick's, nose spray, throat spray, more steroids, NyQuil [and] a screaming baby in the middle of the night.

"I have never phoned in a single tour, I have an impeccable record for not cancelling... I'm doing the absolute best I can."

The star's stage show is a physically demanding spectacular

Most fans have been sympathetic towards the singer, whose hits include So What, Just Like a Pill and Get the Party Started.

"She can't help being sick," wrote Michelle Hansell. "Give her a break, she's human just like the rest of us. Get better soon."

"I doubt anyone is more disappointed or upset than Pink is herself. Give her a break guys!" added fan Jessica Robinson.

"Hope you feel better soon," said Keryn. "You still amazed and blew us away on Saturday night in Sydney even though you were still sick. What a champion effort! Please take care of yourself."

Others fans expressed anger that Monday's show had been called off just hours before Pink was due on stage.

"Pink just cancelled again with people already lining up," wrote Shanie on Twitter.

"Just found out tonight's concert is postponed, after 9 hours travel and a night to stay Sydney," said Russ Silversmith.

Yet others said it would be unwise for the star to undertake her physically demanding show, which involves high-wire acrobatics, while feeling unwell.

"It's good #pink cancelled," said Nicole. "You don't want someone flying above the audience with gastro."