MANILA - Large parts of the Philippine capital are in the grips of a water crisis, as a dry spell begins draining a main source.

For over a week now, long queues of people have waited for hours in front of water trucks, deep wells and stores selling distilled water across metropolitan Manila.

More than 13 million people live in Metro Manila, which spans 16 cities and one town.

Pasig and Mandaluyong, two cities with a total population exceeding 1.1 million, are now looking to declare a "state of calamity", so they could use emergency funds to source for more water, buy more lorries and come up with other contingencies.

All of Mandaluyong's 27 districts are suffering through 20-hour-long water service interruptions.

One district has had no water at all for eight days. There, every night, residents run out of their homes with all sorts of water containers whenever a fire truck appears.

This week, water rationing was extended to more cities being serviced by privately held concessionaire Manila Water.

Taps ran dry for long stretches of the day for Manila Water's more than six million customers.

The National Kidney and Transplant Institute, a government hospital north of Manila, was forced to stop water supply for its hospital rooms, so it could continue running its 70 dialysis machines.

Another government hospital, in Pasig, cut surgical procedures by half, as its water reservoir nearly went empty.

First responders reported that fire hydrants had gone dry.

In recent days, there had been a mad rush to buy pails that could hold at least 30 litres of water. A clerk at one of the nation's largest retailers of household and sundry goods said a restaurant owner cleaned up the store's entire stock of large pails and plastic drums.

Distributors of distilled water had stopped taking calls, and car wash operators had shut down.

Police stations and jails were buying more water containers for inmates held in their cells.

A cleaning staff at SM North Edsa, the country's largest mall, said toilets at two floors were closed.

Not even senior government officials have been spared.

President Rodrigo Duterte's spokesman Salvador Panelo told reporters he was in the middle of taking a shower when the taps suddenly went dry.

The situation has not been this bad since the government privatised water distribution in Metro Manila in 1997.

Taps are running dry because Manila Water, which supplies half of Metro Manila, has not have enough water sources to cover growing demand.

"This is really a supply deficit issue," said the company's president Ferdinand de la Cruz.

Manila Water draws 1.6 billion litres of water a day from Angat dam, in Bulacan province, north of Manila. In recent years, though, it has had to supply 1.75 billion litres a day, as the population in its concession area grows.

To cover for the shortfall, Manila Water has also been drawing water from the much smaller La Mesa dam.

With a recent long dry spell, however, the water level at La Mesa plunged to its lowest in 21 years, and Manila Water could no longer draw sufficient volume from it.

Demand surged after Manila Water announced supply interruptions last week and set off hoarding.

Government regulators are blaming Manila Water for failing to augment its capacity and tap new sources and for relying solely on La Mesa and on water rationing.

The company's officials retorted that this was because the government sat on its requests to build more reservoirs and water treatment plants, as well as proposals to build a new dam, to be funded by China, to augment the capital's water sources.

Congress is stepping in. Separate committees of the Senate and the House of Representatives are set to probe the water shortage next week.

Leftist groups said they would lead a class suit against Manila Water.

Manila Water said the situation would return to normal when the rains come.

To that, Manila Cardinal Luis Antonio Tagle exhorted the country's 100 million Catholics to pray for rain.

"Let us together storm the heavens with our supplication, that God's mercy be upon us and send us the rain we need," he said in a letter to clergymen.