MANILA (AFP) - The Philippine police have arrested an Australian man over the "brutal" murder of a Filipina teenager he met on the Internet after her body was found in a motel room, officials said on Wednesday.

The remains of 17-year-old Alona Alvarez were found by employees at a motel in the southern city of Dipolog on January 30. Tourist Ali Ali, 42, confessed to killing the teenager "in self-defence", saying his "mind went blank", the police said.

The pair had met in Dipolog for the first time just two days before the murder after talking online. The police said Ali flew to the Philippines purposely to meet Alona. "Her face was so unrecognisable and horribly disfigured, the mortician had a hard time," police investigator Ronald Dingas told AFP. "She suffered a very brutal death. It's too much."

Alona had deep head wounds, had lost most of her teeth, and suffered a brain haemorrhage which ultimately led to her death by acute resipiratory failure, Mr Dingas said, citing a police autopsy. She was naked, and investigators also found sex toys and marijuana in the room.

Motel staff told the police the Australian had checked into the room with Alona two days earlier, Mr Dingas said.

Ali was arrested on Sunday in the city of Dumaguete, 75km away from Dipolog, Dumaguete police chief Superintendent James Gofoth told AFP.

The suspect, his knuckles heavily bruised, told the police he attacked Alona after the victim bit his penis when asked to perform oral sex, Supt Gofoth added.

"He said she bit his penis and even showed his penis to us," Supt Gofoth said.

"He said he did it out of self-defence. He said his mind went blank."

"He was planning to escape to Manila," the officer added.

Ali was brought back to Dipolog where the police filed a murder complaint against him before the local state prosecutor.

He faces a 40-year prison term if found guilty. A court appearance has not been scheduled.