A man accused of helping a Philippine gunman kill seven people and wound 12 others has been detained as police investigate the motive for the drug-fuelled rampage, officials said Saturday.

Witnesses told police the arrested suspect helped reload a semi-automatic pistol as the gunman, later killed by police, went house to house Friday looking for neighbours to shoot at a slum in Kawit town outside Manila.

Police arrested John Paul Lopez in Imus town near Kawit late Friday, hours after gunman Rolando Bae was killed in a firefight with police, national police spokesman Generoso Cerbo said.

"We are investigating the level of his involvement, but definitely he faces criminal charges," Chief Superintendent Cerbo said of the alleged accomplice.

Lopez, the caretaker of Bae's house, said he was blameless because the gunman forced him at gunpoint to load the clip of the .45-calibre pistol between the shootings, Cerbo told AFP.

"If that is proven false, he would be charged with many murders," Cerbo added.

The arrested suspect tested positive for methamphetamine, an illegal stimulant, said Kawit police investigator Plaridel Daprosa.

He told AFP the authorities were looking into the possibility that the murder spree, which police said was preceded by a four-day drug and alcohol binge, was triggered by problems in Bae's marriage.

"That's a possible reason that we're looking into. We know that the couple split a few months back," Daprosa added.

Cerbo, the national police spokesman, said 12 people were being treated for gunshot wounds in hospitals in Manila and Cavite following the rampage.

Police said a pregnant woman and four children were among those shot, and that two of the children had died.

They said Bae, whom police believe to be in his early 40s, had been an elected member of the village council but left the community after being defeated in a 2010 ballot for the post of village chief.

Bae and Lopez began their drink and methamphetamine binge on New Year's Eve, according to governor Juanito Victor Remulla, governor of Cavite province where Kawit is located.

Derrick Carreon, spokesman for the Philippine Drug Enforcement Agency, said that drug use may have played a role in the killings, explaining that frequent methamphetamine use can lead to anti-social or even psychotic behaviour.

"They may start seeing demons during withdrawal. You take it from there," he told AFP Saturday.

Methamphetamine is the most commonly used narcotic by the nearly two million illegal drug users in the country, Carreon added.

Friday's shooting rampage followed the New Year's Eve deaths of two children by celebratory gunfire in Manila, which has triggered outrage and condemnation of the Philippines' poorly enforced gun laws.

There were 1.2 million registered firearms in the country last year, with another 600,000 unlicensed weapons in circulation, according to police.

But pro-gun lobby spokesman Ernesto Tabujara said Saturday it was unfair to punish licenced firearms owners like himself with a gun ban for the shooting deaths in Kawit as well as the two young victims of stray bullets in Manila.

Less than one percent of gun crimes in the Philippines were committed by licensed gun owners, said Tabujara, secretary-general of Pro-Gun Philippines.

"We feel we have an inadequate number of policemen protecting our citizens... Our 125,000 policemen could not possibly guard and protect 100 million Filipinos," he told AFP.

"In the critical moments before the police arrive (at a crime scene), homeowners have a right to protect themselves and their families."