Mozambique's government has urged many people to immediately seek higher ground after at least five people were killed in Cyclone Kenneth.
Authorities fear flooding and mudslides in the days ahead after heavy rain lashed the region.
Nearly 700,000 people could be at risk, with many left exposed and hungry as waters rise.
Mozambique's disaster management agency said one person had died in Pemba city and another in hard-hit Macomia district, while residents on Ibo island said two people died there.
Details on the fifth death were not immediately available.
Nearly 3,500 homes in parts of the country's northernmost Cabo Delgado province were partially or fully destroyed, with electricity cut, some roads blocked and at least one key bridge collapsed.
Some schools and health centres were damaged.
"There's a very intense strip of destruction where the wind first made impact in coastal districts," Nicholas Finney, response team leader with the aid group Save the Children, told The Associated Press after visiting Macomia district.
The team found people in shock in a region where a cyclone had never been recorded in the modern age.
Terrified children and traumatised parents "face a huge task to start to rebuild", he said.
Rain is forecast over the next several days and Mozambique's meteorological authority said the storm could potentially move back out to sea and intensify again, Mr Finney added.
"It doesn't look good, quite honestly," he said of the risk of flooding.
As water levels rose, Mozambique authorities asked residents of Mecufi and Chiure districts and parts of Macomia and Muidumbe districts to immediately seek higher ground.
Some rivers in the region have burst their banks in the past, notably in 2000.
Cyclone Kenneth arrived late on Thursday, just six weeks after Cyclone Idai ripped into central Mozambique and killed more than 600 people.
This was the first time in recorded history that the southern African nation has been hit by two cyclones in one season, again raising concerns about climate change.
The remnants of Kenneth, which packed the power of a Category 4 hurricane, could dump twice as much rain as Idai did last month, the UN World Program has said.
Some forecasts warned of as much as nine inches of torrential rain, or about a quarter of the average annual rainfall for the region.
The International Federation of Red Cross and Red Crescent Societies reported heavy damage to Cabo Delgado province, with the communities of Macomia, Quissanga and Mocimboa da Praia of highest concern.
Communications remained challenging in some areas as authorities and aid groups scrambled to assess the damage, especially in more far-flung communities in the largely rural region.
"The situation wasn't worse thanks to awareness-raising work by local authorities," Mozambique's disaster management agency said.
People left homeless tried to patch together shelters from the rain.
"I'm looking for someone to lend me a porch so I can clean it up and stay with my family," one Macomia resident, Wild Eusebio, told the Portuguese news agency Lusa.
Another family of 13 people, including eight children, was living in an improvised plastic tent, the report said.