Public support for President Rodrigo Duterte is starting to crumble.

Outrage over the thousands killed in a bloody anti-crime drive, allegations of hidden wealth and a months-long war with terrorists in Marawi city have dragged his popularity to its lowest since he took office in June last year.

A poll by respected pollster Social Weather Station published on Sunday showed that the President's net satisfaction rating fell 18 points to 48 per cent in the third quarter of the year, based on a survey of 1,200 adults from Sept 23 to 27. His trust rating also dropped to 60 per cent, down 15 points.

"That is quite a huge drop. It reflects growing dissatisfaction with the direction of his drug war and perceived uncertainties over the overall direction of the country," said political analyst Richard Heydarian, author of The Rise Of Duterte: A Populist Revolt Against Elite Democracy.

Tellingly, the biggest decline - by some 30 points - was seen among the poorest, who supported Mr Duterte because he promised to end crime and corruption in six months. But his anti-drugs drive has drawn flak for targeting the poor rather than drug kingpins.

Police say at least 3,900 drug suspects have been killed in purported shoot-outs. Human rights activists say the number is closer to 13,000. Most of those killed were small-time drug dealers and users.

A poll in June showed that three in five Filipinos believe only the poor were being killed, and that many suspects were not resisting arrest when they were gunned down. The death of a 17-year-old in August stirred public anger after security footage showed what appeared to be images of police dragging the teen minutes before he was shot dead.

"The poor are turning bitter on the drug war," said Mr Heydarian.

There have been other missteps.

Mr Duterte is being dogged by allegations that he and his family have millions' worth of undeclared wealth. Opposition politicians have also accused him of derailing congressional probes into the smuggling of 6.4 billion pesos (S$170 million) worth of illegal drugs that have entangled one of his sons.

The conflict in Marawi, which began when hundreds of Islamist extremists stormed the city on May 23, is also fuelling discontent, especially among Muslims. More than half of Marawi lies in ruins, and patience is wearing thin among the 200,000 forced to flee the city.

Mr Duterte's critics were quick to take advantage of the survey slump.

"It's very encouraging to know that the Filipino people are beginning to see the light. They are now seeing Duterte for who he really is: a lying, rude, amoral, corrupt and oppressive former mayor who is totally incompetent about governance at the national level," said Senator Antonio Trillanes, who has been pushing to investigate the drug war killings and the President's bank accounts.

For Associate Professor Eduardo Araral, vice-dean at the Lee Kuan Yew School of Public Policy, the survey results "should serve as a wake-up call". Mr Duterte should look into delivering on his promise to prosper the poor, he said.

Mr Heydarian believes Mr Duterte can reverse the fall.

"Recalibration and tinkering with his policies here and there could still lead to a rebound. He isn't an unhinged demagogue," he said.