LONDON: A Pakistani mother and four of her children were killed Monday in a suspected arson attack on their home outside London, police said.

Sabah Usmani and her sons Sohaib, 11, and Rayan, six, as well as 12-year-old daughter Hira, died in in their end-of-terrace home in Harlow, Essex, in what firefighters described as “harrowing scenes”.

A third son, Muneeb, nine, died in hospital while Maheen, a three-year-old girl, remains in a critical condition in a specialist burns unit.

“In the history of Essex Police, seldom has there been an incident of this gravity, in which five people, four of them children, have lost their lives,”Assistant Chief Constable of Essex Police Gary Beautridge told a press conference.

Detective Superintendent Rob Vinson said the police were investigating “to see whether this fire was started deliberately”.

The children's father Abdul Shakoor “fought hard to save his family in appalling conditions”, Beautridge said. Shakoor, who works as a doctor, was treated for minor injuries.

Originally from Karachi, the family lived in Saudi Arabia for more than a decade before moving to Manchester and then the town of Harlow in Essex.

Firefighters said some kind of fuel may have been used to ignite the house since the blaze spread so quickly, starting downstairs and soon reaching the family asleep upstairs.

A burning car was also found near the house, and although it did not belong to the family, it too is being treated as arson. Police said the family may not have been the intended target of the attack.

Parvez Hamid who knew the couple since they moved to Harlow, said: “The Asian community is very tight-knit in this area and we are all in shock.

“Their children were so well behaved and I was always envious that mine weren't the same,” Hamid said.

The children's mother was also a doctor who stayed home to take care of her children.