British police say 58 people are missing and presumed to have died in this week's blaze at a west London highrise apartment building.

"Sadly at this time, there are 58 people who we have been told were in Grenfell Tower on the night that are missing and therefore, sadly, I have to assume that they are dead," Cmdr. Stuart Cundy told reporters on Saturday, adding that the figure could change.

This latest figure, based on reports from the public, included the 30 already confirmed to have died in the fire in west London early Wednesday.

Cundy said there may have been people in the tower that police are not aware of, which would add to the death toll.

He said it will take "weeks or longer" to recover and identify all the dead in the social housing building that was left charred and gutted by the devastating blaze.

Demonstrators hold up banners during a march in North Kensington on Friday, the same day The Guardian reported that contractors installed a cheaper, less flame-resistant type of panelling than what was available during a renovation that ended in May 2016. (Toby Melville/Reuters)

He reiterated there is a police investigation underway and that it will look at how the fire spread.

"It will look at the building itself."

Cundy promised an "exhaustive investigation" into the tragedy and said "my heart goes out to those affected."

Prime Minister Theresa May met Saturday at 10 Downing Street with the families of some of the victims, along with volunteers and community leaders from the North Kensington neighbourhood where the building caught fire.

She visited the site of the fire on Latimer Road on Thursday, speaking to first responders. May returned to the neighbourhood the following day to meet with survivors at St. Clement's Church while angry protesters waited outside. Some shouted "coward" as she left by a side door.

Protesters on Friday were prevented from entering the upper floor of the Kensington town hall where they demanded to speak to local officials and shouted 'we want justice.' (Toby Melville/Reuters)

May announced on Friday that her government has set up a £5 million ($8.4 million Cdn) "discretionary fund" to help pay for food, clothing, personal supplies and funerals. The U.K. government has also promised to find homes for the survivors within three weeks at the latest.

​Residents of the tower say May was far too slow to visit the stricken community, that the building had been unsafe, and that officials have failed to give enough information and support to those who have lost relatives and their homes.

Survivors and families of the victims are demanding answers in light of reports that external panelling put up during a recent renovation contributed to the flames' rapid spread.