Storm Frank has disrupted travel after heavy rain and winds of up to 80mph swept across Northern Ireland on Tuesday night and Wednesday.
More than 270 roads were blocked by floods or fallen trees. Most have now reopened but some remain impassable.
The Belfast to Dublin rail service was also disrupted due to flooding between Newry and Portadown.
Meanwhile, emergency crews worked overnight to restore electricity to almost 21,000 homes and businesses.
In part of County Down, half a month's rainfall fell in just three hours.
According to the Department for Regional Development, the worst affected area was around Katesbridge in south Down, with the heaviest downpours between 04:00 GMT and 07:00 GMT on Wednesday.
Across Northern Ireland, there was less rainfall overnight but it still amounted to a quarter of the average rainfall for December.
Environment Minister Mark H Durkan has activated an emergency payment scheme for people whose homes have been badly affected by flooding.
Agriculture Minister Michelle O'Neill said hundreds of workers from the Rivers Agency, local councils, roads authority Transport NI, the Northern Ireland Fire and Rescue Service (NIFRS) and the drainage authorities worked through the night to lessen the impact on homes and businesses.
She said roads across Northern Ireland and a "small number of properties in Down, Armagh and the greater Belfast area" had been affected by the storm.
"Pumping is ongoing at Derrychara Link in Enniskillen to keep the road passable. Rivers Agency is also pumping at Greenbank in Newry to ensure the high tide which coincides with increased river flows does not cause problems," she said.
Ms O'Neill said about 4,200 sandbags had been distributed and flood response staff had dealt with 80 calls for assistance.
The roads authority Transport NI dealt with 150 incidents on Tuesday night, mainly involving fallen trees.
In County Down, the A1 southbound was closed for hours between Dromore and Banbridge due to flooding but has now reopened.
Police are warning motorists to drive slowly, to be prepared for debris and unreported fallen trees, and not to drive through flood waters.
Sara McClintock, of NIE Networks, which manages the power network, said considerable damage had been caused by fierce winds.
"Storm Frank came through with a real bang and it affected all across Northern Ireland," she said.
"They were difficult conditions to work in."
She added: "Trying to climb poles and replace poles in very heavy rain and strong winds is not easy.
"Equally, it's important for the general public to be aware of that safety message as well.
"Obviously if somebody sees a broken pole or a broken line, we would tell them not to approach it, but to call us immediately."
Ms McClintock said if homeowners or businesses are without electricity, they should contact NIE Networks either by phone on 03457 643643 or online at nienetworks.co.uk.
Passengers on nine flights into Belfast International Airport were temporarily held on planes due to high winds on Tuesday night.
Two other inbound flights from Luton and Tenerife had to be diverted to Dublin.
P&O ferry sailings from Northern Ireland ports are operating, while all flights from Belfast City Airport and Belfast International Airports are scheduled to arrive and depart on time.
Storm Frank has also caused disruption to travel networks and power supplies in the Republic of Ireland.