Over 24 million in the Philippines' economic hub entered a lockdown Monday amid warnings from officials that the week-long restrictions could be extended if COVID-19 infections do not slump.

With the exemption of essential workers, people have been ordered to stay indoors as Metro Manila, the national capital region, and four neighbouring provinces struggle to contain a surge of infections that has brought hospitals to their knees.

The Epidemiology Chief at the Health Department, Alethea de Guzman, warned that coronavirus lockdowns could be extended to bring out a "sustained" drop in cases, only hours into the latest lockdown imposed on the region.

"All options are open," said Defence Secretary Delfin Lorenzana, who chairs the government's COVID-19 task force.

More contagious virus strains have been blamed for the record spike that has taken Philippine's caseload to more than 720,000.

Traffic crippled the streets of Manila early Monday as police attempted to ensure only essential workers were traveling.

However, reporters saw officers periodically open up the roads to ease congestion.

"It's difficult since it's no work, no pay," said residnt July Calma, as she walked home after attempting to pay her water bill but finding the office closed.

"We don't [have savings] because we spend it every day."

The tighter coronavirus restrictions affect a fifth of the country's population, with church services and other mass gatherings banned, a 6pm to 5am curfew in force and public transport reduced. Additionally, supermarkets, pharmacies and other essential businesses are allowed to operate, and outdoor exercise is permitted.

The lockdown was announced Saturday by presidential spokesman Harry Roque, who initially suggested public transport would be halted.

A prior months-long lockdown crippled the Philippine economy, cost millions of jobs and left many households hungry.

Roque said the decision to tighten restrictions again was "very delicate" and acknowledged extending the lockdown could lead to more people dying from hunger and other non-coronavirus-related illnesses.

In turn, the Budget Secretary Wendel Avisado said assistance would be available for nearly 23 million people under lockdown -- almost everyone affected -- but did not offer any further details.