Local police in Olongapo City, a province in northern Philippines, are doing round-the-clock investigation work to gather evidence that could point to the motive of the death of an Australian beach resort general manager who was killed at gunpoint to his temple on Friday night.

A .45 calibre pistol was fired and sucked the life out of 53-year-old Queenslander Paul Dean Davy, general manager of budget hotel Blue Rock Beach Resort. He was shot right in front of stunned diners, who were mostly foreigners.

The brutal murder reportedly occurred "in the middle portion of the Blue Rock restaurant, in the customer-receiving area," Fairfax Media quoted Olongapo police officer Tyrone Tecson as saying. He was currently talking then with the resort's co-owner, looking out over the shoreline.

"The attacker approached from behind and shot him and immediately left the scene," Mr Tecson said. The attacker, believed to be of Filipino appearance, was wearing a blue cap and glasses. He looked somewhere between 30 to 35 years old.

"It's a nasty experience," Mick Hay, owner of the Blue Rock Beach Resort in Olongapo, near Subic Bay, was quoted by the Sydney Morning Herald. "I was sitting right next to [Paul] when he got shot."

Police have yet to have conclusive evidence behind his death, but believed Mr Davy knew his assailant. Authorities came up with the theory as it was only recently that the budget hotel sacked a number of employees. Police surmised the killer could have been a disgruntled former staff.

"There is no angle involving drugs or a love triangle with a woman," Mr Tecson said. "We are looking at the employees who have been fired or forced to resign."

Nasser Abdulasul, another Olongapo Police officer, said interviewed hotel staff remarked Mr Davy was known for being harsh. "Some of the staff told us that there were some workers who had been laid off recently without compensation. So that is one motive," he was quoted by the Sydney Morning Herald.

Police have found the white scooter which the gunman used to fled the scene. It was found 3km from the crime scene. Police are now trying to locate the owner of the scooter.