A human sea of Catholic pilgrims flooded the Philippine capital on Monday to join a religious march, police said, defying government warnings of a potential terror attack on the annual festival.
Barefoot men and women wearing maroon shirts waved white towels and handkerchiefs as the "Black Nazarene", a life-size icon of Jesus Christ carrying a cross, was paraded on the capital's streets.
National television aired live footage of a huge crowd at Manila's Rizal Park at the start of a procession that is expected to last until early evening.
The Philippines is the largest mainly Roman Catholic nation in Asia, a legacy of the country's Spanish colonial past.
The "Black Nazarene" march is one of the most spectacular of many religious festivals that feature throughout the year, and police estimated between two and three million people turned up on Monday to be part of the crowd.
Many Filipinos attribute miraculous powers to the icon, which a Spanish priest brought to the Philippines in 1607.
The huge turnout came amid a warning by President Benigno Aquino on the eve of the festival that authorities had uncovered a plot to attack the event, potentially with a bomb triggered by a mobile phone.
"The sad reality of the world today is that terrorists want to disrupt the ability of the people to live their lives in the way they want to, including the freedom to worship and engage in community activities," Aquino said.
National Security Adviser Cesar Garcia said Monday that authorities were looking for up to nine people from the southern Philippines who could be involved in the plot.
He and other officials did not specifically identify the potential attackers, but the southern Philippines is well known as being home to a wide range of Islamic militant groups.
While at least 80 percent of the Philippines' population of 94 million are Catholic, about another four percent are Muslim.
Most of the Philippines' Islamic minority live in the south, and Muslim rebels have been waging a decades-old armed separatist insurgency that has claimed tens of thousands of lives.
One of the most infamous Islamic militant groups is the Al Qaeda-linked Abu Sayyaf, which is blamed for the country's worst attacks including the bombing of a ferry in Manila Bay in 2004 in which more than 100 people died.