The surviving boy was left with “life-changing injuries”, Essex Police said.

He was taken to Colchester General Hospital and later transferred to a specialist unit.

The boys’ mother also sustained minor injuries in the attack after being bitten by the animal. The force said the dog had been put down.

Latest updates after baby killed by dog

Officers were called to investigate the attack at the property in Harwich Road onThursday afternoon.

Tributes including flowers and toys have been left outside the house. One card left with a bunch of roses read: “RIP little man.”

The attack comes just eight weeks after three-year-old Dexter Neal was bitten by an American bulldog in Halstead, Essex.

A woman was arrested and bailed in connection with that incident.

Police said no arrests had been made so far in connection with the Colchester attack.

Ch Insp Elliot Judge described the baby’s death and his brother’s injury as a “tragic incident” and said officers were supporting the family.

Police would not confirm the dog’s breed but said it had been put to sleep “with the consent of the owner”.

Neighbours told the BBC the family had only recently moved to the area.

One, Dave Thompson, said: “The first thing I noticed was an armed response vehicle.

“I saw what must have been the first ambulance roar off under police escort.”

He said police backed into the drive of the house to “recover the animal” which he described as a “Staffordshire bull breed”.

“It was alive and not aggressive when they brought it out of the house and put it into the back of the van. It was quite big, I think it was a cross-breed.

“Everyone had been pushed back by the police and a woman came out of the house first,” he said.

Another neighbour, Scott Mills, who lives in a house opposite, described how passing schoolchildren gathered to witness the aftermath of the tragedy.

“There were a lot of children about because of the time – a lot of children were coming home from school,” the 24-year-old said.

He described the dog removed from the house as “not a normal Staffie. It was a lot more chunky, probably a Staffordshire-cross or some kind of bulldog breed”.

Mr Mills added: “No-one opposite knows the family but I wish them the best at this awful time.”

Will Quince, MP for Colchester, tweeted: “So sad to hear of the death of a baby in a dog attack in Colchester. My thoughts and prayers are with his brother now at Colchester Hospital.”

He later tweeted to say he understood the boy had been transferred to a “specialist unit”.