Security fears and a potential storm had Philippines leaders on edge ahead of the arrival today of Pope Francis on his first visit to Asia's largest Catholic nation, where millions of people are expected to attend public events.

Church bells will toll across the Philippines, a mostly Catholic nation of about 100 million people, when Francis arrives on the final leg of his week-long Asian tour at about 5.45 pm.

However, the Philippine weather bureau expects a tropical storm will dump heavy rain on Francis's devoted followers, who are already thronging the streets in anticipation of his arrival.

Francis will bring a message of compassion to millions of poor Filipinos suffering from the effects of corruption, decades-old insurgencies and climate change, as well as the problems faced by the families of the 10 million-12 million Filipino migrant workers overseas.

He will visit the central province of Leyte, which is still struggling to recover from Typhoon Haiyan that killed 6,300 people in 2013. About two million people are expected to attend an open-air mass on Saturday at Tacloban City airport, almost completely destroyed by Haiyan.

In Manila, around six million people are expected to hear Francis say Mass at Rizal park, the largest in the capital, on Sunday, probably exceeding the record crowd of 5 million during Pope John Paul II's 1995 World Youth Day Mass.

The government has declared a three-day public holiday to clear traffic in Manila, a city of 12 million people, and has even closed financial markets.

On Wednesday, President Benigno Aquino personally inspected motorcade routes and public venues, which were lined with black-and-white concrete barriers topped by thick wire mesh to control eager crowds.

Interior Secretary Manuel Roxas said Aquino was willing to serve as Francis' "personal bodyguard" to ensure his safety. In a televised address on Monday, Aquino appealed to Filipinos to follow security rules after two people were killed in a stampede during a religious procession on Friday.

Nearly 50,000 soldiers and police from across the Philippines will be deployed in the country's biggest security operation. In 1970, a Bolivian artist dressed as a priest tried to stab Pope Paul VI when he arrived at Manila airport.

In 1995, a group of Islamist militants conspired to assassinate Pope John Paul II in Manila, a plan uncovered by police after an accidental fire in the militants' rented apartment.