The crime scene would “remain in place over the coming days”, the force said.
Officers have appealed for anyone with any information to contact them.
A spokesman said: “Whilst this is a fast-moving investigation, we are at the early stages of establishing exactly what has occurred and why.
“Detectives are continuing to work to establish a motive.
“However, we don’t believe there is a wider threat to the community.
“We will provide further updates when it is appropriate to do so.”
A woman who lives nearby, but did not want to be named, said it was a shock to hear of the deaths.
“It is awful,” she said.
She said early on Monday morning, her daughter had returned from work and told her there was an ambulance and police at the top of the road.
Then her granddaughter told her they were still there “and a white tent was up in the street and [the police] are going to be there a few days”.
She said many older people lived in the neighbourhood. They “just live… and don’t want any trouble”, she said, adding it was normally a quiet area.
“It is not like this. I mean you get police here now and again, but not like this. Not at all.”
Another woman, who said she has lived in the area for 17 years, echoed her shock at the fatal stabbings nearby.
The woman, who also did not want to be named, said she did not know the deceased people personally, but “they have been round here a long time”.