BANGKOK: Pope Francis has shrugged off security concerns for his visit to the Asian bastion of the Catholic faith, ditching his bulletproof ''Pope mobile'' for a white open-sided jeepney, the most common form of transport in the Philippines.

The pontiff will greet devotees from the specially built vehicle bearing the papal coat of arms and Vatican State registration plates during part of his visit to Manila, where up to six million people are expected to attend a Sunday mass in a waterfront park.

Philippines military chief Gregorio Catapang says Pope Francis's visit from Thursday night to Monday in the country with 75 million Catholics ''will be the greatest security nightmare that we can have''.

In a nationally televised address President Benigno Aquino urged Filipinos joining papal events to remain calm and avoid creating a stampede, the biggest security concern for the visit.

''I ask you, do you want history to record that a tragedy involving the Pope happened in the Philippines?'' he said.

Filipinos have prepared a welcome with rock-star intensity for the 78-year-old leader of the 1.2 billion-strong Catholic world whose face beams from life-size cut-out images in malls and churches, posters, shirts, coins, stamps, coffee mugs among hundreds of mementoes.

Streets have been cleaned and welcome banners are hanging from electric posts, billboards, hotels shops and restaurants.

''Every step he makes, every car ride he takes, every moment he stays with us is precious for us,'' said Archbishop Socrates Villegas, president of the Catholic Bishops' Conference of the Philippines.

Gregory Gaston, rector of the Philippine Pontifical College in Rome, said ''it will be like a father visiting his children; the Pope will visit people hit by calamities - victims, people suffering.

''It can be an opportunity to renew the faith of the biggest Catholic nation in Asia,'' he said.

The Pope will travel to Tacloban on Saturday, the town hardest hit by Super Typhoon Haiyan in 2013. He will share lunch with 30 survivors of frequent disasters in the island nation.

Extraordinary security measures will be imposed at papal events, especially Sunday's mass in Manila's Rizal Park, which organisers say is likely to attract the biggest crowd ever to attend a papal mass.

Backpacks and umbrellas will be banned while police officers required to remain at their posts for hours will wear adult nappies.

Up to 40,000 police, soldiers and volunteers will be deployed to protect Pope Francis in the country where a plot by al-Qaeda terrorists to assassinate Pope John Paul II was foiled during a visit in 1995.

Snipers will sit on rooftops, aerial cover will be provided by the Philippine Air Force and sniffer dogs will roam where the Pope is due to appear.

The church says the theme of the visit will be ''mercy and compassion''. There are hopes among many Catholics the Argentina-born pontiff will listen to pleas to change the church's strict traditional approach to issues such as contraception and sexual morality.

The Philippine government last year started giving thousands of poor families access to contraception for the first time. The church strongly fought the measure but many Catholics supported it as a way to reduce the country's high birth rate and poverty.