Guwahati: The fire broke out suddenly and turned massive within minutes, according to witnesses.

Four-year-old Ivan Goswami was to celebrate his birthday in a big party on Thursday evening but it never happened. He was charred to death along with his seven-year-old brother Ishan in a massive fire at their home in Guwahati.

The boys were playing alone on the first floor of the house in Baishthapur and their mother, grandmother and helps were on the ground floor, preparing for the birthday party in the evening.

The fire broke out suddenly and turned massive within minutes, according to witnesses.

The boys' mother Silpi Goswami, grandmother and two domestic helps were busy with the party arrangements when the first floor burst into flames. Before they could do anything, the brothers were trapped in the blaze, say sources.

The fire could have started because of short-circuit, said Guwahati Commissioner of Police MP Gupta. A preliminary investigation suggests an LPG cylinder also exploded, making it worse.

Police sources said after the children were extricated from the first floor, they were taken to Gauhati Medical College and Hospital, where the doctors declared them dead.

Their mother and grandmother have also been injured and are in hospital. Their condition is stable but both are believed to be in trauma.

The children's father, Tushar, a geologist, was on his way back from Sivasagar, about 355 km away, when the unspeakable tragedy took place.

The fire was so intense that the first floor of the duplex was almost completely razed.

Assam chief Minister Sarbananda Sonowal has ordered a magisterial probe into the incident after neighbours alleged that fire engines reached late.