A Melbourne man who pleaded guilty to carelessly driving his rented jet ski into his girlfriend in Phuket has released an emotional letter explaining his decision and his “unbearable sorrow”.

Thomas Keating, 21, will have to stay in Thailand while a Thai court processes the charge, but he is not being detained.

On Sunday, his jet ski collided with another craft being ridden by his 20-year-old girlfriend, Emily Collie from Kyabram, causing severe neck and shoulder injuries.

Lifeguards tried unsuccessfully to revive her on the beach.

“First and foremost, I would like to express my unbearable sorrow at the loss of my soul mate, Emily, who I loved more than anything else in this world, as well as my never-ending apologies and condolences to Ian and Sally Collie and the rest of their family,” Mr Keating wrote in a statement released by the Australian Government to media.

“They have my heartfelt gratitude for the love and support they have shown me while they are coping with the most devastating loss imaginable.

“This was a tragic accident … however I take full responsibility for what happened.

“I have decided that the best thing is to accept a charge of careless driving leading to death.”

Mr Keating asked for privacy for the two families, and thanked consular staff in Thailand.

Emily’s parents, Ian and Sally Collie, said in a statement earlier this week they didn’t believe anyone was at fault for Emily’s tragic death.

“This was a tragic accident. We do not believe anyone was at fault,” Ian and Sally Collie said in a statement.

“In particular, we do not place any blame on Tom Keating, who we care about very much and we know loved Emily deeply,” they said.

“We are all heartbroken beyond words, and at this extremely sad time we wish to be together with our family, with Tom, and with other loved ones to grieve and celebrate Emily’s life.”

Mr Keating met with Thai police at the Phuket’s Karon Police station on Thursday.

He said glare on the water from the setting sun had impaired his vision.

Karon Police Chief Colonel Sanya Thongsawad told Phuket News that during the seven hours of questioning Keating accepted a plea of guilty.

Col Sanya said Mr Keating told investigators a large wave surged while they were zig-zagging, causing the two jet skis to collide.

“Accepting the charge is a good thing because the sentence will be reduced,” he said.

The careless driving charge carried a possible penalty of 10 years jail, but it is expected any sentence imposed will be suspended.

– ABC, with AAP