Three men have been arrested amid allegations that staff at two care homes were victims of modern day slavery.
Gwent Police and the National Crime Agency (NCA) carried out warrants at Danygraig Nursing Home in Newport and Ashville Residential Care Home in Brithdir on Thursday morning.
Two Newport men, aged 53 and 64 and a third from Surrey, 43, are in custody.
A reception centre for potential victims has been set up.
A number of police remain outside Ashville Care Home and officers are also focusing on a nearby house where local people have said a group of up to 13 women live, according to BBC Wales reporter Nelli Bird, who is at the scene.
One neighbour said they saw police arrive at the house at around 06.30 GMT.
The neighbour, who did not want to be named, said: "I went to have a nose through the window. There was a lady stood there on her own.
"Then about half hour later two men came. They were going to put the door through but then they let them in through the back.
"[The women] are back and forth, they're always dragging suitcases around.
"There are men coming back and forth. They're always partying in there.
"The youngest looks about 18, oldest could be 40 or 50."
Det Ch Supt Nicky Brain said: "The offences that are being investigated are serious...
"We would like to reassure [residents and their families] that this investigation is not as a result of any concerns raised regarding crimes committed against people residing in these homes."
Gwent Police said officers from its human trafficking team were working with partner agencies including the British Red Cross, the Salvation Army and New Pathways.
In a joint statement, Newport council and Caerphilly council said they were working with Aneurin Bevan University Health Board and Care Inspectorate Wales to "ensure a continuation of care".
"We appreciate families may be concerned as a result of today's events but we would like to reassure them that their loved ones are safe and their well-being is our priority," it continued.
Modern slavery is defined as the recruitment, movement, harbouring or receiving of children, women or men through the use of force, coercion, abuse of vulnerability, deception or other means for the purpose of exploitation.
It is a crime under the Modern Slavery Act 2015.