Mother's Day is always tough for Clarita Alia, whose four teenage sons were believed to be killed by vigilante squads, but this year even more so as the man she blames is close to becoming president.

Alia, 62, lives a bitter existence in a shanty town in the southern city of Davao, with a gutter running through her kitchen and only fading photos of her sons who were murdered between 2001 and 2007 after various run-ins with the local police.

Davao is the long-time domain of Rodrigo Duterte, the tough-talking lawyer who has surged to become the favorite to win Monday's presidential elections.

He has threatened to abandon human rights laws and kill suspected criminals across the country.

Duterte, 71, is promising to clean up the Philippines with the same methods he employed in Davao, a city of nearly two million people that he has ruled as mayor for most of the past two decades.

Millions of Filipinos have embraced his authoritarian line, as they seek a savior to the chaos and corruption that dogs their lives. Roughly one quarter of the nation's 100 million people live below the poverty line, and crime is rampant.

But Alia wants to warn other Filipinos of the dangers she believes Duterte would bring to the nation if he rises to the presidency.

"I don't want him to become president," Alia, one of the few people willing to speak out publicly against Duterte in Davao, told Agence France-Presse on Sunday as mothers around the world celebrated being with their children.

"He doesn't have any morals. God forbid if he becomes president. So many children will be victims."

Duterte is accused of running death squads in Davao that summarily executed suspected criminals.

Human rights groups say the squads -- made up of local police, former communist rebels and hired assassins -- have killed more than 1,000 people.

Alia's sons were aged between 14 and 18 when they were killed. She and rights groups believe they were murdered by the death squads, after police warned the boys they were on hit lists.

'FORGET HUMAN RIGHTS'

Duterte has at various times acknowledged his involvement in the death squads, and on one occasion boasted of them killing 1,700 people. At other times he has denied any knowledge of them.

But he has repeatedly made it clear on the campaign trail that thousands of people will die if he becomes president, as he unleashes security forces with shoot-to-kill orders in a bid to achieve the seemingly impossible goal of eradicating crime in six months.

"Forget the laws on human rights," Duterte said in his final campaign rally on Saturday night in Manila.

"If I make it to the presidential palace, I will do just what I did as mayor. You drug pushers, hold-up men and do-nothings, you better go out. Because as the mayor, I'd kill you."

On an earlier occasion he vowed that 100,000 criminals would die in his crackdown, and so many would be dumped in Manila Bay that the "fish will grow fat" from feeding on them.

President Benigno Aquino, who is limited by the constitution to serving a single term of six years, launched a desperate bid in the final stages of the campaign to derail Duterte, accusing him of being a dictator in the making and likening him to Hitler.

"I need your help to stop the return of terror in our land. I cannot do it alone," Aquino said in an appeal to voters in Saturday's final rally for his preferred successor, Mar Roxas.

But many Filipinos appear ready to sacrifice the rule of law for what they hope will be a safer society. Duterte goes into Monday's election with a big lead over Roxas and Senator Grace Poe, the adopted daughter of movie stars.

"It's nothing," Grace Quiniones, a market stall vendor in Davao and Duterte fan, told AFP when asked about his promises to kill thousands of suspected criminals.

"He doesn't kill people who are not criminals. Only those people who break the law disappear, like drug pushers."