Residents have been urged to stay away from homes flooded after a "blow out" at a mine shaft following reports some had returned against advice.
Eighty people had to be evacuated from Skewen, Neath Port Talbot, on Thursday and the Coal Authority is investigating the cause of the flooding.
On Sunday First Minister Mark Drakeford visited the village.
Specialists said mine shafts in the area were stable, but villagers were told it was not safe to return home.
Neath Port Talbot Council tweeted on Sunday afternoon that some evacuated residents had ignored the warnings.
It said: "We are getting reports that some residents who have been evacuated are returning to their homes.
"Investigations are ongoing at the site, including safety checks by utility companies. They have asked us to reiterate the request for residents to stay away and that it is not safe to return today or tomorrow."
I visited Skewen earlier today to see for myself the damage caused by serious flooding.— Mark Drakeford (@fmwales) January 24, 2021
My thoughts are with all those affected by this incident.
The @WelshGovernment is working with @NPTCouncil, @CoalAuthority & others to assess the cause and extent of the damage. pic.twitter.com/1fiZDmv7oy
It is not known how many residents were thought to have returned to their flooded homes or how long they were there for.
Bigger equipment is being brought in to "understand in detail what has caused the blow out", according to Coal Authority chief executive Lisa Pinney.
The Coal Authority, which manages the effects of past mining on communities, said it believed the "blow out" was likely to have been caused by a blockage underground which caused water to back up before breaking out.
Council leader Rob Jones warned residents it was unlikely that they could return home by Monday.
Ms Pinney said a hand-drilling crew "determined the precise location and extension of the collapsed mine shaft" on Saturday.
"This now allows us to bring in larger equipment to investigate the wider mine workings and drainage channels in the area around it, so we can understand in detail what has caused the blow out," she said.
"We have checked all recorded shafts in the immediate area and found them all to be safe.
"We will be checking over a wider area in the days ahead."
During his visit to the village Mr Drakeford was shown the sinkhole which had opened up on Thursday, leading to the flooding.
On Friday the Welsh Government confirmed financial support would be made available to people affected by the floods, up to £1,000 per household.
Mr Drakeford said on Sunday: "Particularly for families who have no insurance, this is a devastating event.
"They will know that the Welsh Government is there to help and we will do that through the local authority which has been here very visibly, helping people in the last couple of days."