Work has started to clear floodwater from Downpatrick after homes and businesses were damaged by heavy rain.
The Department for Infrastructure (DfI) said it needed water levels to drop in the River Quoile before pumps could be used to clear the water from the town centre.
A number of towns in counties Down, Armagh and Antrim have been impacted by the downpours this week.
SDLP MLA Colin McGrath said Downpatrick had witnessed "apocalyptic scenes".
He added about 25 businesses around Market Street had been "decimated".
Earlier, DfI said it understood how difficult the situation was for residents and businesses and "we appreciate their patience as we work with partners to manage the situation".
The department also said conditions in Portadown are expected to improve as the level of the River Bann falls.
Reporting from Downpatrick on Friday, BBC News NI south-east reporter Cormac Campbell said business owners were waiting "to see what has become of their livelihoods".
In Newry, he added: "The floodwaters have receded from the Sugar Island area and the big clean up has begun, with the smell of spilled oil prevalent".
The director of Downpatrick and County Down railway museum said the flood had been an "absolute disaster", which had left his site inaccessible to volunteers.
"In the 40 years we have been there, we have never seen anything remotely like this," Jonathan King told BBC Radio Ulster's Talkback programme.
"The entire site is under water, between about one foot and five feet plus."
Mr King said he hoped there would be tailored financial support for charities as well as businesses.
"There's not much that anyone can do at the moment, I went up to the site this morning and I wasn't able to get anywhere near it at all."
Karen Sherwin, whose family has had a florist business in Newry for 60 years, described it as a "disaster zone".
"We are on our hands and knees, the place is not even safe," she told BBC News NI.
"There are electrics, there is oil, there is sludge, it is terrible. Every day I am closed, it is just heartbreaking."
Ms Sherwin said stock she ordered from the Netherlands for the shop in Sugar Island had to be sent back, following the flooding.
"It is a week old, it is no good to me, it is fresh produce, it is flowers, I just can't get over it."
'Millions of pounds in damage'
Eamonn Connolly, Newry Business Improvement District Manager, told BBC News NI's Evening Extra programme he believed the damage caused to businesses from the flooding could run into millions of pounds.
Newry Courthouse is set to reopen from Monday, according to the Department of Justice.
It was closed as a temporary measure due to severe flooding in the area.
October 2023 was the wettest month ever in Armagh since records began in 1838, according to Armagh Observatory.
A number of homes in the Portadown area of County Armagh have been damaged by flooding in recent days, with roads closed and transport services affected.
Brendan McCann told BBC News NI his house had been left in "a mess".
"I don't know whether I'll ever be able to do anything with it or not or whether I'll be able to come back to it again or not," he said.
Amanda Best, who has lived in her home for 30 years, said: "You just come in and it's devastating".
"I've never faced the like of this in my life," she explained.
The Northern Ireland Executive Office said on Friday a recovery sub-group has been established bringing together civil service departments and local government.
It said this would engage with businesses affected by the severe weather and keep political representatives informed.
"Departments are also exploring what financial support they could collectively provide as part of the overall response," a spokesperson said.
"An approach will be made to HM Government, through NIO (Northern Ireland Office), for financial assistance for impacted businesses."
The Department for Communities is providing emergency £1,000 payments for domestic properties which have been flooded.
A Northern Ireland Office spokesperson said the UK government has been "in close contact" with the civil service and would continue to work with it closely "in the days ahead".