A fire that engulfed a London apartment block, killing at least 79 people earlier this month, started in a fridge freezer, police in the U.K. city said Friday.

Det. Supt. Fiona McCormack said the Hotpoint model, FF175BP, was not subject to recall and that the manufacturer was doing further tests.

"We now have expert evidence that the fire was not started deliberately," McCormack said.

Whirlpool, the company that owns the Hotpoint brand in Europe and Asia, said it is helping authorities get all the information needed for the investigation.

Police said both the insulation and tiles used in cladding at the 24-storey Grenfell Tower block failed all post-fire safety tests.

"Preliminary tests show the insulation samples collected from Grenfell Tower combusted soon after the test started," McCormack said.

Such were their concerns after the tests that the information was immediately shared with government to disseminate more widely.

"Given the deaths of so many people, we are considering manslaughter as well as criminal offences and breaches of legislation and regulations," McCormack said.

The June 14 blaze, Britain's worst since the Second World War, has heaped pressure on Prime Minister Theresa May, already fighting for her political survival after her party lost its parliamentary majority in a snap election on June 8.

When speaking about the 79 people who died, are presumed dead or missing, McCormack said: "I fear that there are more." 

McCormack encouraged anyone who lived at the tower to speak with police, no matter their immigration status.

"I do not want there to be any hidden victims of this tragedy,"McCormack said.

She also encouraged residents to tell police about any safety concerns they've had.

The night of the fire, emergency services received over 600 calls, she said.

"Some of those calls are over an hour long and each call tells its own distressing story."

Police have received CCTV footage and over 70 images from the fire, and will install an elevator on the outside of the building to aid in their investigation.

"There is a terrible reality that we may not find or identify all those who died due to the intense heat of the fire," McCormack said, adding that police are working with as much sensitivity as possible.

"It is impossible to learn about what happened that night without feeling the true tragedy and the human cost of this terrible, terrible incident," she said.

With files from CBC News