POLICE are yet to find the motive behind the horrific stabbing death of a two-month-old baby in a suburb south of Brisbane.

Qianqian “Queenie” Xu was allegedly stabbed by her grandfather at the family’s home in Parkinson about 2.30pm yesterday.

Her grandmother and mother, Yuanyuan Cao, 28, originally from Luoyang in China, were also stabbed. Ms Yuanyuan’s partner George was working at the time of the attack.

This afternoon, Detective Inspector Tony Duncan told a media conference investigators were still searching for answers as to why the tragedy unfolded.

Det Insp Duncan said the baby’s father was at work when police believe the grandfather started stabbing the trio.

The father, a small-business owner, did not know his child was dead until detectives told him.

He is being comforted by family.

Det Insp Duncan said there were no recent incidents at the home to point to such a horrific turn of events.

“The father actually expressed his surprise that something could happen,” he said.

The grandparents had travelled to Australia from China in December as the baby’s mother prepared to return to work at a bank and needed help with childcare.

They had previously been in the country in September for the birth of the child.

Det Insp Duncan said the grandfather was out of intensive care and is expected to speak with police in the coming days.

The grandmother is still in intensive care, and the mother is recovering and has spoken with police.

No charges have been laid at this stage.

EARLIER: A two-month-old baby girl died last night after a stabbing frenzy in which her grandfather allegedly attacked her, his wife and his daughter.

Qianqian “Queenie” Xu was allegedly stabbed at the family’s house at Parkinson in Brisbane’s south about 2.30pm yesterday by her grandfather, who was visiting from China.

VIDEO: Grandfather’s dramatic arrest

PREVIOUSLY: How tragedy unfolded

Neighbours told of hearing screams as the incident unfolded in the quiet street.

Police believe the baby’s mother, 28, escaped the home on Watheroo Place and alerted residents at a house on an adjoining street before police were called.

The child’s grandmother, who was visiting Australia with her husband, was found unconscious in the house with life-threatening injuries.

Police found the grandfather, 53, in the front yard of the property with life-threatening injuries, which police believe may have been self-inflicted. All three underwent surgery last night.

An argument inside the home is alleged to have sparked the stabbing, and blood was seen around the garage doorway and driveway of a home.

Detectives were last night were planning to use a translator to speak to the baby’s mother.

Distraught police had to be relieved at Lady Cilento Hospital last night, where the two-month-old baby was taken before she died.

Sun Gill, who lives behind the home, said he heard the screams while he was outside.

“I was outside feeding my dogs when I heard the screams, they were very loud,” he said.

“I ran outside down the street then and I saw him (the grandfather) walking down the street with blood pouring from him.

“When I saw him outside, he was losing a lot of blood. When we saw him in the street, he then stumbled into a neighbour’s front yard.”

One neighbour said they often saw the couple walking their dog outside.

“I came outside and saw him in handcuffs on the driveway dripping blood, it was unbelievable,” she said

Detectives set up a major incident centre in Acacia Ridge last night, which included officers from the homicide squad.

Inspector Sean McKay said interviewing the victims would be key to the investigation.

“At this stage detectives are currently investigating the incident to ascertain exactly what has occurred here,” he said.

“One of the victims went to the secondary location which is Mapleton (Court) and that’s where police have been notified from there.’’

A community vigil will be held in the neighbourhood tonight.

It will take place at the Watheroo Place Park from 6.45pm to 7pm following the tragic incident.

Councillor Angela Owen-Taylor said she received a number of requests for a community gathering overnight.

Locals were this morning distributing letters to neighbours urging them to come along.