The storm, the worst to hit Mozambique in at least a decade, had windspeeds of more than 200 kilometers per hour before it made landfall early Friday.
Local officials said that this week's heavy rains had already claimed 66 lives, injured 111 people and displaced 17,000 people.
In their response, humanitarian agencies want to focus on providing education, health, WASH, food security, protection for the vulnerable who include women and children, and nutrition.
Most of the deaths occurred in Beira - a port hub and capital of Sofala province - a city which has virtually been cut off after power lines crashed, the airport was shut and roads swamped by flooding.
Tropical cyclone Idai battered central Mozambique on Friday, killing at least 19 people there and cutting off more than half a million in Beira, one of the country's largest cities.
Zimbabwe state television station, ZBC, reported that 150 people are missing.
Cyclone Idai: DEADLY Cyclone Idai strikes central Mozambique - How many have died?
"The information we have so far is that over 100 people are missing and some of them" may have died, Joshua Sacco, a member of parliament in Chimanimani district, told AFP. "There were people inside", he told AFP, saying they were listed as missing.
Zimbabwe's opposition Movement for Democratic Change spokesman Jacob Mafume tweeted that there is a "serious humanitarian crisis" unfolding in eastern Zimbabwe districts.
Zimbabwe's ministry of information has been posting updates on social media and has announced that the country's national army was leading rescue efforts in the affected areas.
As the cyclone hit, Mozambique's President Filipe Nyusi appealed for emergency assistance for the victims before leaving for eSwatini. "Houses and trees were destroyed and pylons downed", an official at the National Institute of Disaster Management (NIDM) told AFP.
South Africa's military has sent in aircraft and 10 medical personnel to help in Mozambique and Malawi, it said in a statement Saturday.
Mozambique's President Filipe Nyusi said the damage is "very worrisome" and said the flooding made it hard for aircraft to land and carry out rescue operations, according to Mozambique's state radio.
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