Four people, including two children, found dead at scene of New Jersey mansion fire being investigated as arson.

The mansion that caught fire near the New Jersey shore is owned by a tech company executive, hours after a blaze also broke out at the house of a relative, officials said.

Video showed smoke pouring from the roof of the two-storey home in Colts Neck as firefighters battled the blaze.

The house is surrounded by fields and has a swimming pool.

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Helicopter footage showed a sheet in the middle of the yard next to the house with police tape cordoning off the area.

Colts Neck is a well-to-do community about 80km south of New York City and is home to horse farms. Typical homes in the town of 10,000 are valued at about US$750,000.

Public records show the home is owned by Keith Caneiro, 50, and Jennifer Caneiro, 45.

The 530 sq m home has four bedrooms and five bathrooms, according to Zillow.

The owners purchased the property in 1998, and the home was built in 2003, public records show.

Caneiro's LinkedIn profile describes him as the CEO and chief technology officer for a company in the New York City area called Square One.

His profile says he graduated from Columbia University with a Master of Science degree in 2018 and previously received certifications from Harvard Business School.

There also was a fire today at a home in Ocean Township, police and prosecutors said. That home, about 16km from Colts Neck, is owned by Paul and Susan Caneiro, and public records show the men are related, sharing at least one address in New York several decades ago.

They are also "friends" on Facebook, but it is unclear how they are related. Paul Caneiro is listed as the vice-president of Square One.

-AP