Fifty-four people were injured when a packed Catholic church balcony collapsed during an Ash Wednesday service in the Philippines on Wednesday, city disaster officials said.

Millions of Filipinos flocked to churches during Ash Wednesday, one of the religion's busiest days, which marks the beginning of Lent in Asia's Catholic outpost.

An 80-year-old woman was critically wounded, the city civil defence chief Gina Ayson told AFP, as another official said most of the other people were slightly injured.

About 400 people were attending mass when the accident occurred at the Saint Peter the Apostle church in the city of San Jose del Monte, near Manila, she said.

Part of the floor caved in, plunging parishioners to the ground floor during Ash Wednesday mass, a city disaster official, Ruben Fortun told AFP.

Fortun said the floor, made of wood "was likely overloaded".

Mayor Arthur Robes has ordered the damaged church shut as investigators inspected the building's structural safety, according to Ayson.

Pictures posted by mayor Robes on his Facebook page showed part of the balcony's wooden floor hanging less than a meter (3.3 feet) from the ground floor, which was littered with plastic chairs and debris.

A yellow police tape was placed across the front of the building, built in 1994, and another photo showed a paramedic inspecting the leg of a man.