Cyclone Kenneth battered northern Mozambique on Thursday with gusts of up to 280 km per hour (174 miles per hour) after killing three people on the island nation of Comoros overnight.
Impoverished Mozambique is still recovering from another powerful tropical cyclone which made landfall further south last month, flattening the port city of Beira and killing more than 1,000 people across a swathe of southeastern Africa.
A regional cyclone-monitoring centre on the French island of La Reunion said Kenneth made landfall at around 2.30pm GMT (2.30am NZT) north of the port city of Pemba and was expected to weaken as it moved inland.
The storm caused storm surges of up to five metres in some areas and rains associated with it could cause serious flooding, the centre said.
"Kenneth remains an extremely dangerous system which is currently severely impacting regions to the north of Pemba," the centre's latest cyclone report said.
A spokesman for Mozambique's National Institute of Disaster Management (INGC) said the government had evacuated 30,000 people from areas likely to be hit by the cyclone.
"The compulsory evacuation process will continue until we have all people in secure ground," INGC spokesman Paulo Tomas said. The INGC said it had food supplies ready to assist 140,000 people for 15 days.
Mozambican officials said on Wednesday more than 680,000 people were at risk from the latest storm. There were concerns that five rivers and coastal waterways could burst their banks, leading to severe flooding.
Government and humanitarian officials did not anticipate the extent of the flooding in the wake of Cyclone Idai last month, and an early warning system implemented did not reach everyone.
Antonie Beleza, deputy national director of Mozambique's Centre for Emergency Operations, told Reuters that this time around the centre had been telling people for days to move out of 17 at-risk districts.
Saviano Abreu of the United Nations humanitarian arm OCHA said the U.N. and non-governmental organisations were assisting the government with a preparedness strategy.
Cyclone Kenneth is expected to linger over Mozambique, dumping rain until late on Monday evening and bringing the risk of more intense flooding, said Dipuo Tawana, forecaster at the South African Weather Service.
In neighbouring Zimbabwe, where hundreds died in heavy rains following Cyclone Idai, the civil protection department sent out a warning that some areas near the eastern border with Mozambique could be affected by the cyclone.
It said people living in low-lying areas including in Masvingo province, Chimanimani, Chipinge, Mutoko, Mudzi and Gokwe North should be on high alert.
US energy firm Anadarko, which is developing large natural gas fields off Mozambique, said it had suspended air transportation in and out of its site as a precaution. Exxon Mobil, also involved in gas fields offshore Mozambique, said it was monitoring the situation.
In Comoros early on Thursday, felled trees and debris from homes were scattered over streets, and houses had their roofs torn off.
The winds caused widespread power outages in the northern part of the main island, Grande Comore, and the capital Moroni as well as on the island of Anjouan, residents said. Government offices and schools were closed.
Kenya Airways said on its Twitter feed it had cancelled flights to Moroni because of severe weather.