Tenants were forced to jump from the roof as flames spread through a rooming house in the Blackfriars area.
One person was arrested and two others were taken to hospital after the fire that police are calling "suspicious."
London firefighters were called to the two-storey rooming house at 15 St. Andrews Street, south of Oxford Street around 9am on Wednesday, where fire had trapped several people on the roof.
"When crews arrived we had an active fire, there was lots of smoke coming from the structure. There was a lot of fire on the exterior of the building as well leading to the second-floor stairwell," said Acting Deputy Fire Chief Jack Burt. "This is a duplex structure where there is one unit above another unit so the only access to the second floor was that exterior stairwell which made it difficult for us to get up, get in and do our searches."
The people on the roof jumped to safety before firefighters were able to reach them. Two of them were taken to hospital with non-life threatening injuries. It is believed between eight to ten people were living in the home.
A damage estimate has not yet been released, but damage to the house is extensive.
Sean Gregory and his cat Smokey.
Sean Gregory lives on the second floor. He said he was awakened to the smoke alarm going off and had to jump out an upper rear window to escape the thick smoke and flames.
"I've been through hell this last little while. I have nowhere to go," said Gregory, who is still recovering from injuries he suffered after being hit by a vehicle last month.
He had been living in the home for just three months and doesn't have renter's insurance.
Clutching his 19-year-old cat Smokey, Gregory noted the furry, grey animal is the only possession he has left and the only one he cares about.
"I don't have a phone now. My credit card, my bank card, my health card, my prescriptions burnt," said Gregory. "I had a beautiful tv, a gold chain I don't care about any of it. I care about my cat."
Firefighters were able to save the feline who jumped back into the burning building after Gregory pulled him out.
A second pet that was inside the house has yet to be located.
Dave Wheeler was asleep in a downstairs room when he heard the commotion.
"I woke up to a bunch of screaming and I went outside and I saw smoke everywhere. The whole entire house was on fire upstairs," said Wheeler. "I lost everything... I am extremely upset right now. Very, very upset right now."
Jim McFadden had just dropped his dog off at the groomer when he happened by the burning home. He parked his truck and rushed over to help.
"There was a lady who had jumped out of the second storey window. She was incapacitated, her leg was broken," said McFadden. "Me and another gentlemen were able to lift her up and bring her across the street and get her away from the house while it was burning."
He said he could see what looked like a burning mattress blocking the only upstairs exit. Standing and watching firefighter's work, McFadden said he didn't think twice about stopping to assist.
"You see a situation, you see somebody that needs help. I am not the kind of person who can stand around and watch. If I can help somebody out of a bad situation I am going to do it," said McFadden.
According to neighbours, there have been three previous fires at the home over the past 12 years. The cause of Wednesday's fire remains under investigation.
"It is very early in our investigation where we are conducting a joint investigation with the London Police Service and the cause of the fire is currently under investigation where we are trying to determine the origin, cause and circumstances of the fire," said Burt.
He anticipates fire officials will be on scene for the rest of the day.
London police officers led a man, who lives in the house, away in handcuffs. Police say he was later released unconditionally.
Those displaced by the blaze are being assisted by the Red Cross.
