Thomas Keating, 22, told police that strong sunlight reflecting from the sea made it impossible for him to see the jet-ski being ridden by his girlfriend, Emily Jayne Collie, who he was holidaying with on the island.

Mr Keating suffered minor injuries when the jet-skis collided off Kata Beach late on Sunday.

Lifeguards pulled Ms Collie, who is from the small town of Kyabram in north-east Victoria, from the water and, with Mr Keating, tried to revive her on the beach before she was pronounced dead at a local hospital.

Thai police lieutenant Patiwat Yodkhwan told reporters on Monday: "Ms Collie's boyfriend, Mr Keating, who was driving the other jet-ski when they collided, will face a charge of reckless driving causing death."

Social media tributes poured in for Ms Collie, who had been dating Mr Keating for 18 months, with one friend posting a photo of the 20-year-old and writing "our dear angel".

"Words can't describe how devastated we are," a friend wrote.

"Rest in peace you gorgeous girl. It's horrible that something as horrible as this can happen, especially to someone you know," another wrote.

Mr Keating's sister, Bree Lyon, told Fairfax Media the family was "absolutely devastated".

"My dearest angel, one you have always been and will always remain," she said about Ms Collie.

"From the very moment I met you I loved you, I cherished your genuine heart, and that beautiful smile. I was inspired by you in so many ways, my darling girl, you were so strong and so determined.

"I miss you so much, Emily. I truly do. I love how you loved my brother, the way you looked into his eyes with nothing but pure love, it was the truest thing I've ever been grateful to witness.

"I promise to look after your Tommy forever and always, our darling girl with those beautiful curls."

Lieutenant Patiwat said the owner of the jet-skis the couple rented did not want any payment for damage to the machines, saying "he wants Phuket to have a good reputation as a holiday destination."

Under an insurance policy that was taken out for the couple's rental, Ms Collie's family will be entitled to a payment of 50,000 Thai baht ($1867).

Her parents are travelling to Phuket to collect her body.

Jet-ski operators usually get people to sign a contract but customers are rarely asked questions about whether they have experience riding them.

Under Thai law, anyone using a jet-ski is supposed to have a "captain's permit" but the law is often overlooked to allow tourists to hire jet-skis.

The death comes at a time Thai tourism officials in Bangkok have been pressing Phuket authorities to make the island safer on the roads and in the water.

But Phuket lifeguards recently had their budget cut.

Australia's smartraveller.gov.au travel advisory warns about the risks of hiring jet-skis and motorcycles on Thai beaches, in particular in Phuket, Pattaya, Koh Samui and Koh Phangan.

"You may be detained and arrested by police following jet-ski and motorcycle accidents until compensation, often in the thousands of dollars, can be negotiated between parties," the advisory says.

Many Australians who take out travel insurance policies in Australia find they are not covered when they have a motorcycle accident in Thailand because they are not licensed to ride one in Australia.

More than 20,000 Australians holiday on Phuket each month.