The cyclone, packing winds of up to 170 kph (100 mph), swept down from the northern part of the country this week, ripping roofs off houses, tearing down power lines and killing at least three people.
Governor Aires Aly of the coastal Inhambane province said most of the affected areas could not be reached by road and telephone communications had been interrupted.
"It is impossible to assess the damage caused by the bad weather. But I can tell you that many houses built with flimsy materials have been destroyed," Aly told Reuters. He said the storm had left an estimated 23,000 people homeless.
In the tourist town of Vilankulo, Mayor Suleimane Amugy said about 95 percent of brick houses had had their roofs ripped off or windows and doors damaged.
"Water and electricity supplies have been interrupted as a consequence of damage to the equipment, it's so terrifying," Amugy told the national state-controlled, Radio Mozambique.
The official meteorological office forecast that Japhet, already losing strength, would dissipate soon.
Japhet is the second cyclone to hit Mozambique this year. Cyclone Delfina killed 47 people and left more that 200,000 people homeless in a country already struggling with severe food shortages after a period of drought.
In 2000, massive floods killed some 700 people and heavily damaged Mozambique's infrastructure.
- Reuters - Thomson Reuters Foundation
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