Aussie teen Lawson Rankin in critical condition after horror accident while on Schoolies in Bali

It was supposed to the trip of a lifetime with friends to celebrate his final school year.

After years of dedication while studying in Newcastle, Lawson Rankin, 18, travelled to Bali for an end-of-year Schoolies trip. But his dream holiday was cut short after a horror accident while riding a scooter left him in a critical condition at the Bali International Medical Centre.

According to his cousin Taren Brown, Mr Rankin was trailing two friends on a motor scooter when a local motorcycle rider snatched a phone belonging to him and sped off.

Mr Rankin, a recent graduate from St Francis Xavier's College, was an experienced rider and so took off around his friends' bike in pursuit of the phone.

But that's when tragedy struck.

Further up the road his friends noticed Mr Rankin's scooter lodged deep inside a concrete drain filled with water. Shining their lights inside the drain, they found him unconscious, facedown drowning in the sewer, his helmet split and his head covered in lacerations.

When the boys jumped into the drain they initially couldn't see Mr Rankin. Once they caught sight of their friend, they lifted him out of the drain and performed CPR to resuscitate him.

Locals called an ambulance, but the high school graduate has been unconscious since.

"This is the most devastating thing a parent can go through, to see our beautiful son in this state in a foreign country is extremely horrific," a family member said in a statement to news.com.au.

"We need to bring him home."

A GoFundMe fundraiser has been set up to support the teenager and his family who have been hit with huge medical costs as a result of the accident.

Mr Rankin has had surgery requiring around 20 stitches for a head wound caused by his crushed helmet. But Ms Brown said the biggest concern for her cousin was the brain haemorrhage he suffered and infection from the water that got into his lungs.

"Thankfully, he has no skull or spinal fractures," she wrote on the fundraising page that has received more than A$100k in donations.

While Mr Rankin's family are by his side in Bali, his recovery journey is unknown.

Despite having travel insurance, Mr Rankin was not licensed to ride a motor bike and the insurance company will not cover any of his medical costs, which are amounting to more than $100,000.

"The bills are already over $30,000 for a few days in an international hospital, and he may not be able to travel for weeks, so this will continue to rise," Ms Brown said.

"Once there is clearance to get him onto a plane, it's expected a Medevac flight to Sydney and transfers to Newcastle to be more than $100,000. Once home, Mr Rankin is likely to have a long journey of rehabilitation.

"It will be one step at a time but an expensive journey."

Mr Rankin is well-known in Newcastle rugby union and rugby league circles.

His family said the support they'd received from friends, family and strangers had been "overwhelming".

"We are so thankful for the boys who saved his life and the love and the support for our son streaming from Newcastle and beyond," the family said.

To donate, head to Lawson Rankin's GoFundMe.