Victoria Police are investigating a “horrific” house fire in Melbourne on the weekend that left a mother and three young children dead.Key points:Arson Squad detectives are still determining the cause of the blazeA man believed to be related to the family is in hospitalNeighbours heard screaming from the houseFirefighters were called to Tulloch Grove in Glen Waverley about 1:40am on Sunday after receiving multiple calls about smoke coming from the two-storey townhouse.Police say Karou Okano and her daughters were found huddled together in the en suite of the home.A man who survived the blaze is in hospital in a critical condition.Crews found the garage on the ground level “engulfed with flames” and the home filled with smoke, Victoria Police Detective Senior Sergeant Neville Major said.”Tragically, four people have perished,” he said.Senior Sergeant Major said police were still determining the man’s relationship to the victims, but it was believed he was related to the family.He was intubated in the hospital and police did not expect him to be able to speak to detectives for at least another 24 hours. Tributes were left for the family near the house following the tragic blaze.(ABC News: Patrick Rocca)Neighbours woken by ‘one big bang’Arson Squad detectives were called to the scene and the exact cause of the fire is yet to be determined.Neighbour Maria Tsakiris said she was woken in the early hours of the morning by “one big bang”.”I thought it was a car accident,” she said.She said when she got near the Tulloch Grove house, she could see ambulances and fire brigades surrounding the property.”It was so, so scary,” she said.About five minutes after hearing the bang, she said neighbours started hearing screaming.”We heard screaming from somewhere, a male’s voice, and that startled me as well,” she said.Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume.WatchDuration: 1 minute 22 seconds1m 22s Residents describe the scenes from the fatal fire as ‘horrific’.Ms Tsakiris said she and her daughter spent two hours on the street near the house, waiting to hear news of the three children before being told they had died.”We were just really upset, really upset,” she said.”It’s just horrific, horrific. It wasn’t even like a fire, it was more like a war zone out here. It was terrible.”Debra and Bianca Ortolan, who live close to the townhouse, said they were woken by smoke filling their home and the sound of explosions.They took in an evacuated family as emergency services worked to bring the fire under control.”[It was] heartbreaking,” Ms Ortolan said.”Not being able to do anything, you’re so helpless … we just all prayed that they got the kids and the mum out.”Fire took two hours to bring under controlWant more local news?We offer tailored front pages for local audiences in each state and territory. Find out how to opt in for more Victorian news.Read moreFire Rescue Victoria assistant chief fire officer Costa Katsikis earlier said crews worked hard to battle the intense blaze in the early hours of the morning.”Upon arrival they were confronted by a fierce fire, a high fire load, a very hot fire that tragically ended in the loss of four lives and one person taken to hospital with smoke inhalation,” he said.”Our thoughts go out to the family and friends impacted by this tragic event.”Immediate neighbours of the townhouse were evacuated and it took more than two hours to bring the blaze under control.Bianca Ortolan said the emergency services did an “amazing job” responding to the fire.Senior Sergeant Major says police treat all fires as suspicious until there is evidence to suggest otherwise.Anyone with information is urged to contact Crime Stoppers.