The incident at Maghera/Draperstown is ongoing and there are no further details.
A NIFR spokesperson said: “We are reminding the public that in the event of serious flooding to phone the NI Flooding Incident Line on 0300 2000 100. If there is a risk to life dial 999 immediately and we will respond.
“We want to reassure the public we are prepared and well-rehearsed in terms of our contingency planning in readiness for the strong possibility of flooding in parts of Northern Ireland across the afternoon and we have redeployed resources accordingly.
“We are working closely with our colleagues in the PSNI, Coastguard and other statutory agencies right across Northern Ireland to assist members of the public.
“We are reminding people of the following safety advice: Do not travel in heavy rainstorms unless absolutely necessary.
"In flooded areas, drivers should not: enter flood water that is moving or is more than four inches deep under any circumstances, drive through fast-flowing water as the car could be swept away
"In more shallow but passable water: slow down, avoid creating bow waves which can damage your car engine; and remember to test the brakes after leaving the water.
"Do not attempt to walk through flooded areas. Even shallow water moving fast can sweep you off your feet and there may be hidden dangers such as: open drains, damaged road surfaces, submerged debris; or deep channels which can result in serious injury or, in the worst cases, death.
"If you do become stranded in flood water and you feel there is a risk to life, dial 999 for emergency assistance.