One of the man daughters, aged 12, rushed to a nearby police station to warn that her father and mother were fighting and he had threatened to burn down the house, Guyana Police Force spokesman Ivelaw Whittaker said.
Police quickly responded and found the building on fire.
"Suspecting that persons were inside, (they) attempted to enter the building, but (were) prevented from doing so by a locked grill door," police said.
The township does not have a fire station and efforts by police and residents to extinguish the blaze with buckets and other receptacles failed.
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The businessman, 50-year-old Linus La Cruz has been arrested. He sustained burns to his body and is under guard at the Port Kaituma Hospital.
The bodies of his wife, Lurlene, 39, daughters Lea, 14, and Lavette, three, and sons Labron, eight, and Levon, one, were later found among the wreckage.
Guyana, a former British colony, is located on the north-east coast of South America and has a population of 755,000 persons.