UPDATE: 4.20pm (AEST)

A family of four, including two children with autism, who were found dead in their northern Sydney home died as a result of a murder-suicide, police say.

Police said it appeared the family died of gas poisoning and are asking the public for help to discover the motive behind the deaths.

The bodies of Colombian nationals Fernando Manrique, 44, Maria Claudia Lutz, 43, and their two children, Elisa, 11, and Martin, 10, were found on Monday morning when police forced entry to the family’s Davidson home.

A NSW Police statement said they had no visible injuries and they were awaiting the results of toxicology reports to determine the cause of death.

“Whilst the cause of death will be a matter for the coroner to determine, police are looking at the possibility the family members died from the introduction of an airborne gas,” the statement said.

“It is early days in the investigation and investigators will need to wait for toxicology results and results of the post-mortems to determine cause of death.

“Forensic police continue to recover evidence from the home in Davidson.”

A large dog was also found dead at the house.

A crime scene is still set up at the home and detectives are back today, searching the backyard and the house.

The homicide squad was looking into the matter, but have handed investigations back to the Northern Beaches Local Area Command.

“Strike Force Josselyn has been established with the assistance of State Crime Command’s Homicide Squad to investigate the deaths,” a statement said.

Northern Beaches Police Superintendent Dave Darcy initially said they were keeping an open mind as to whether they were searching for a suspect, but police have since ruled out this possibility.

Superintendent Darcy said the family were valued members of the community.

“The mother in particular is held in very high regard in the community,” he said.

“Since coming to Australia they’ve made a significant contribution to how we live, they’ve done a fantastic job.”

EARLIER

A family of four, including two children with “significant disabilities”, has been found dead in a home in Sydney’s north, in what police have described as a “tragic” and “horrific” event.

Officers attended the home on Sir Thomas Mitchell Drive at Davidson about 11.20am on Monday following reports concerning the occupants’ welfare.

Northern Beaches Police Superintendent Dave Darcy said officers found a 43-year-old female, a 44-year-old male, a 10-year-old boy and an 11-year-old girl dead at the home.

Fernando Manrique with his daughter Elisa. Photo: Facebook: Fernando Manrique

The family has been identified as Colombian nationals Maria Claudia Lutz and Fernando Manrique, and their children Elisa and Martin.

Superintendent Darcy said “a large dog” was also found dead at the house.

Superintendent Darcy described the incident as a “tragic” and “horrific thing”. He said “both children suffer a significant disability”.

The ABC understands the children had autism.

“It’s extremely confronting, the officers – we consistently have these concern for welfare cases, and unfortunately in some cases this is what the police are confronted with,” Superintendent Darcy said.