Firefighters were called to Park Road at about 20:00 GMT on Friday and spent the night working to protect pensioners' bungalows from flooding.
The River Corcrain burst its banks overnight and about an inch of water flowed into the houses.
Pensioner Brendan McCann said every room in his house was affected.
He said the river level was rising from noon on Friday and started to flood the street outside his home.
The water started to come into his bungalow at about 04:00 GMT.
"All floors are flooded - bedroom and kitchen and the whole lot," Mr McCann said.
A number of other residents told the BBC their furniture had been damaged, as they gathered bags of belongings and left their flooded homes.
The Northern Ireland Fire and Rescue Service (NIFRS) said their crews used specialist equipment, including high volume pumps, in a bid to divert water away from the bungalows.
Portadown-based firefighters were assisted by crews from Lurgan, Pomeroy, Armagh and Belfast.
The police, staff from the Northern Ireland Housing Executive, Rivers Agency, Transport NI and emergency planners from the local council were also present throughout the night.
The Northern Ireland Fire and Rescue Service (NIFRS) has issued a flood safety warning to members of the public.
They advised people to "exercise extreme caution entering flood water", either in a vehicle or on foot, for any purpose due to the high risk and unpredictability in these circumstances".
About six homes have been damaged by flood water after a river overflowed in Portadown, County Armagh, during the early hours of Saturday.