A British tourist left in a coma after falling ill on holiday is stranded overseas after her insurance company refused to cover treatment and medical evacuation, her family says.

Heather Maskell, 62, was on holiday in Cancun, Mexico when she got sick but because she didn’t declare a new asthma medication, her insurers won’t cover her costs.

Ms Maskell became ill with a severe bacterial chest infection and was rushed to hospital on advice from the onsite doctor at Cancun’s Hard Rock Hotel, The Sun reported.

She was eventually put into an induced coma and ventilator as she was unable to breathe on her own.

Ms Maskell finally woke up but her family claim British insurance company Barclays/CEGA had withdrawn funding for her treatment and special transport home despite initially authorising payment.

The family have started a GoFundMe page in a bid to raise £135,000 ($A246,000) to get her medically evacuated back to the UK.

Writing on the page, Ms Maskell’s niece Sian Sponge Crossland claimed the insurers withdrew funding because she had not declared preventive medication she was issued for asthma in 2017.

She said the family were initially unsure whether her aunt would ever wake up from her coma after falling ill on September 12.

“The doctors expected my aunty to wake up within 48 hours of withdrawing sedation, but she didn’t,” she said.

“My mum flew out to Cancun on the 21st of September to be with her as we didn’t think she was going to wake up.

“By some miracle she did wake up on the 25th of September. She is still very weak but is recovering from her infection slowly and will need rehabilitation to help build back up the muscle loss she has from being in the coma.

“Her medical insurance company Barclays/CEGA authorised funds for treatment on the 12th of September.

“However, on the 27th September they then withdrew authorisation for funds naming the reason as her not declaring a preventive medication that she was issued in 2017 for asthma.”

Ms Maskell went to Cancun every year, her sister Linsey Webb said.

She has chronic obstructive pulmonary disease and asthma, both of which “are accepted pre-existing conditions and well managed — she can walk for miles”.

In a heartbreaking plea for help, niece Sian said her aunt was retired and needed a special medical evacuation air ambulance but did “not have this kind of money available” to pay for it.

“We can provide medical documents, photos, pretty much any reassurance that is needed to prove this is a genuine plea for help,” she said.

A Barclays spokesperson said: “We are working with our insurance provider to ensure Ms Maskell’s claim is resolved as soon as possible and she receives the care she needs at this time.”

This article originally appeared on The Sun and was reproduced with permission