Tropical Storm Freddy, one of the most powerful storms ever to hit the southern hemisphere, has killed 190 people in Malawi after ripping through southern Africa for the second time in a month, Malawi's disaster management agency says.

The commercial hub of Blantyre was the hardest hit district and severe flooding and rains have broken roads and bridges, hampering relief operations.

Freddy has also left a trail of destruction in Mozambique after it made landfall for the second time over the weekend.

The death toll in Malawi has jumped to 190 from 99 reported on Monday, the Department of Disaster Management Affairs said.

It added that 584 people have been injured and 37 are still missing as heavy rains continued to pummel the country.

Families in Blantyre were counting the cost of the storm as they waited to collect the dead bodies of relatives from the Queen Elizabeth Central Hospital mortuary.

The flooding and rains have hit rescue operations and made it difficult to get relief to those affected, aid agencies said.

"It's a challenging operation in the sense that there's been incidents of mudslides and so people are getting stuck in those mud accumulations," Estere Tsoka, emergency specialist at UNICEF in Malawi, saidl.

"People are trying to find a place to hang in there for some time."

Freddy pummelled central Mozambique on Saturday, ripping roofs off buildings and bringing widespread flooding around the port of Quelimane before moving inland towards Malawi with torrential rains that caused landslides.

The full extent of the damage and loss of life in Mozambique is not yet clear.

Freddy first developed near Australia in early February and is set to be the longest-ever recorded tropical cyclone.

The United Nations' weather agency has convened an expert panel to determine whether it has broken the record set by Hurricane John in 1994 of 31 days.

with AP