Just a week after Tropical Storm Ana left a trail of destruction through Madagascar, the United Nations warned Friday that an incoming cyclone could impact nearly 600,000 people.

Cyclone Batsirai is expected to make landfall on Madagascar's east coast on Saturday morning, after passing through Mauritius.

"We anticipate a significant impact in Madagascar, including in areas that are still recovering from Tropical Storm Ana in late January," Jens Laerke, spokesman for the UN's humanitarian organisation OCHA, told reporters in Geneva.

He said the UN and aid organisations were ramping up their preparedness, placing rescue aircraft on standby and stockpiling more humanitarian supplies.

At least 131,000 people were affected by Ana across Madagascar. More than 58 people were killed, mostly in the capital Antananarivo.

Some 71,000 people in Madagascar were displaced by that storm, the UN said, warning that many of them risked being impacted again when Batsirai hits.

The UN's World Food Programme (WFP) pointed to estimates from national authorities that some 595,000 people could risk being directly affected, and 150,000 more might be displaced due to new landslides and flooding.

"We are very nervous," Pasqualina Di Sirio, who heads the WFP's programme in Madagascar, told reporters by video-link from the Indian Ocean island.

She said evacuations were ongoing from some of the areas most at risk, and that the authorities had prepositioned boats and other material to help rescue people if they are trapped.

WFP meanwhile has prepositioned food to provide aid, and also masks to help limit the spread of Covid among the displaced, she said.

The International Federation of the Red Cross and Red Crescent Societies also voiced deep concern Friday that Batsirai could significantly worsen the humanitarian situation in a country already grappling with a prolonged hunger crisis.  

It warned that 4.4 million people across the country could be at increased risk, due to the cyclone.

The UN's World Meteorological Organization (WMO) warned the approaching cyclone risked intensifying from a category 3 to a category 4 storm, with experts describing it as "very dangerous".

WMO spokeswoman Clare Nullis told reporters the cyclone was expected to have an impact even before it hits Madagascar, with waves at sea expected to reach up to 15 metres (50 feet), and a possible storm surge of up to 1.5 metres in some coastal areas.