According to the Some 200,000 people are reportedly in danger in Pemba alone, while the situation in the northern towns of Macomia and Quissanga is said to be very critical, with worries that the island of Ibo will be cur-off.
Cyclone Kenneth struck the southern African nation last week with winds of 220km/h (140mph), flattening villages and damaging thousands more homes.
The storm lost strength, but torrential rain was still battering the area on Monday, with more expected.
As a result, flights have been grounded – hindering the aid effort.
It is predicted the weather system will dump twice as much rainfall as Cyclone Idai, which struck last month, leaving more than 900 dead across Mozambique, Malawi and Zimbabwe.
The flood risk was compounded by Kenneth hitting at the end of the rainy season when river levels were already high, the UN Office for the Co-ordination of Humanitarian Affairs (Ocha) noted.
Already, Pemba, the regional capital of Cabo Delgado state, has experienced more than 2m (6.5ft) of rain and flooding.
Attempts to reach some areas have not been entirely successful.
“We managed to send one flight with World Food Programme (WFP) supplies of rice and biscuits, and some non-food items,” Mr Abreu told news agency AFP.
“But unfortunately the weather conditions are changing too fast and threatening the operation. It’s raining again and the second flight couldn’t go.”