A ball of fire and explosions ripped through a munitions depot at the Philippine army's headquarters near the financial district in Manila Wednesday, injuring 25 people, mostly soldiers and firemen, officials said.

The blaze is suspected of triggering the blasts that rained bullets, broken bricks, pieces of concrete, glass and tree branches at the sprawling Fort Bonifacio site, they added.

"I was a few metres (yards) away when the fire broke and caused a loud explosion," army spokesman Lieutenant-Colonel Noel Detoyato told reporters.

He put the updated toll at 25 injured, many of them soldiers as well as firefighters who were trying to put out a blaze at the isolated munitions depot when the entire building suddenly exploded in orange flame.

Footage by local television network ABS-CBN showed the main explosion, followed by soldiers and firemen running and shouting for help on a football field strewn with injured colleagues, tree branches and other debris.

Colleagues shouted at a fireman in a fire retardant suit who vainly tried to pull his fire hose out of the inferno while soldiers and other firemen loaded injured colleagues into an ambulance and an army truck.

The building is surrounded by trees and is located a few minutes' drive from the Makati financial district.

Detoyato said a barracks nearby was used as quarters by army explosives experts who respond to bomb alerts and similar emergencies in the capital.

The cause of the blaze was being investigated, he added.

Detoyato said the army had ordered the evacuation of nearby offices and commercial buildings as a precaution, though no more explosions occurred and the fire was eventually put out.

An AFP photographer saw seven men being treated for various injuries at the army hospital.

"We were hit by flying bricks and broken glass as we retreated from the building," volunteer Manila fireman Agrifino Santos told AFP.

The 40-year-old fireman said his team was dispatched from a nearby district and were trying to put out the late morning blaze when the huge explosion occurred.

"We hit the ground immediately but we got hit nonetheless," said Santos, his head heavily bandaged and his back scorched after his shirt ignited.

His six colleagues had apparently less serious cuts on their legs and hands.

Philippine Army deputy spokesman Captain Anthony Bacus told reporters he was in a nearby building when he heard a series of small blasts "like firecrackers" shortly after the fire alert was raised.

"After about 15 minutes there was a huge explosion," he added.