The rally edged towards violence when protesters tried to break through lines of police, who were carrying riot shields and wooden batons, to reach the summit venue.

Pacific leaders' summit on Thursday, enraging some demonstrators but amusing others.

Hundreds of left-wing protesters rallied outside a venue where US President Barack Obama and other leaders of the 21-member Asia-Pacific Economic Cooperation (APEC) group were meeting.

The rally edged towards violence when protesters tried to break through lines of police, who were carrying riot shields and wooden batons, to reach the summit venue.

Police responded by firing water cannons and scuffled with protesters who were chanting: "Junk APEC".

Then police pulled out their secret weapon: pop princess Katy Perry on giant loudspeakers.

Perry's hit song "Roar" was played at full volume, the top of a demonstration disco playlist aimed at distracting the protesters and drowning out their chants.

Dolly Parton's "Islands in the stream", David Guetta's "Sexy bitch" and the Bee Gee's "How deep is your love" were among the other songs deployed against the protesters.

To add a street bass beat, some of the police tapped their batons against their shields in time with the music.

"It's ridiculous," leftist member of parliament Carlos Isagani Zarate told AFP, as the protesters retreated to soul classic "My Girl".

Many other protesters also expressed anger at authorities trying to suppress their message of opposition to globalisation and free-trade policies championed by APEC.

"We just want to make our voices heard," 64-year-old mango farmer Candelario Rusasena told AFP.

But others could not hide their amusement.

"That was a rude and desperate move," 54-year-old rice farmer Redo Pena told AFP as he broke into a toothless grin.

Metro Manila police spokeswoman chief inspector Kimberly Gonzales told AFP the music was aimed at de-escalating tensions.

"Filipinos in general love music and it has a calming effect for everyone. This goes well with our maximum tolerance policy during protests," Gonzales said.

The Philippines has a famous music culture, with karaoke one of the most popular forms of entertainment across all sectors of society.

It is not uncommon for tourists to encounter taxi drivers, supermarket cashiers and airport security staff spontaneously breaking out into song.

Filipino musicians are also a staple of hotel and cruise ship bands around the world.

And prisoners at the main jail in Cebu, the Philippines' biggest city, have become an Internet sensation by posting videos on Youtube of them dancing to Michael Jackson's "Thriller".

Police spokeswoman Gonzales said using music at protests was not an unusual tactic, and there was no intent to trivialise Thursday's rally.

"We understand the seriousness of the issues. We don't mean to insult people," she said.

The protests occurred as Philippine President Benigno Aquino was welcoming Obama, Chinese President Xi Jinping and other leaders for the summit's second and final day.

The protesters said they opposed APEC's free-trade agenda because it favoured big corporations and neglected the poor.

"Aquino should protect his people, globalisation has caused the prices of our goods to go down. We barely break even," 47-year-old rice farmer Nida Floresca told AFP.

"We don't even have irrigation to water our crops. Aquino should think of us first."

Floresca came with several neighbours from their farming town in La Union around 300 kilometres (180 miles) north of Manila. They marched in sandals and straw hats.

One police officer estimated the crowd of protesters at about 2,000, although there were no official numbers given.

More than 20,000 police and soldiers were deployed this week to ensure security during the APEC summit.

Philippine authorities said they had already been planning the nation's biggest ever security operation for the meeting, which was ratcheted up even higher after last week's deadly terrorist attacks in Paris.