Three terraced houses and a conservatory were caught up in the flames and have have been left seriously damaged, while a fourth house was filled with smoke during the blaze in Temple Way, Tividale.
Two people were treated by paramedics at the scene but nobody was seriously injured in the fire which started at 11am on Friday and took around two hours to extinguish.
Investigators believe the blaze was caused by the sun's rays passing through a magnifying lens attached to a craft lamp.
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Part of Temple Way was cordoned off by police following the blaze as crews dampened down the site where the roofs of the two of the houses were left needing to be stripped and replaced.
More damage was seen from the rear of the properties where a gaping hole was left in one home.
The fire broke out at one of the terraced houses before spreading to two adjoining properties.
Among the affected houses, one was owned by Stella Allen, 61, who was at work in Coventry at the time.
She was alerted to the blaze by her neighbour. Her cat was inside the house at the time but escaped when firefighters opened the door.
She said: "I am just shocked. My neighbour Fred called me saying 'I think you better come back, your house is on fire'.
"Then I rang my daughter (Sarah Deans, 40, from Rowley Regis) because she would get here quicker.
"I had to come back from work. My manager told me to go home."
Stella said she would assess the damage of her home but was planning to stay with her daughter.
She added: "My cat ran out when firefighters arrived. It was one of my cat's nine lives."
Sarah added: "Apparently the fire started in the conservatory. It has subsequently spread to their side."
Asked if anyone was injured, she said: "I have no idea. Apparently they were on their way out (when it happened)."
Stella and Sarah were joined by another resident as they sat on garden chairs, watching the firefighters at work from across a small patch of grass outside Stella's home.
Behind them by about 50 metres, a police cordon was set up stopping traffic.
Behind the houses, from MacMillan Close, the worst of the damage could be seen, with the first floor of one of the houses left gutted.
A hydraulic platform was in use while a large hose pipe was transporting water from a drain and a nearby water source.
Some residents gathered outside their front doors watching the aftermath.
One of them was Bal Gill, 47, who saw the fire take hold and the flames quickly spread.
He said: "I could see the smoke from the conservatory.
"I heard a bang and phoned the fire brigade.
"Literally, in a couple of minutes, the fire has gone 'woosh'."
He added: "You don't see something like this every day. It spread quickly to the next door."
A spokesman for West Midlands Fire Service said: "Crews were mobilised and on scene in under five and a half minutes and were met with a severe fire involving a terraced block of four houses. The fire had broken through the roof and spread, affecting three houses within the block.
"Our crews worked hard using assertive firefighting tactics were able to prevent the spread to the remaining property.
"The fire was quickly brought under control and one occupant and a neighbour suffered minor injuries and were given initial on-scene treatment by firefighters, before being transferred to the care of on scene paramedics.
"Eleven fire appliances, one hydraulic platform around 35 firefighters along with specialist officers are currently on scene working with colleagues from ambulance, police and utility companies to make the buildings and surrounding community area safe.
"Crews will be remaining on scene for the remainder of this afternoon, working with fire investigation officers to locate and understand the cause of the fire, which at this stage is still unknown."
A West Midlands Ambulance Service spokesman said: “We were called by the fire service at 11.14am to a fire in Temple Way, Tividale. We currently have one ambulance and a paramedic officer at the scene.
"We’ve treated two patients, one for minor injuries and the other for smoke inhalation. Both have been discharged at the scene.”