What you need to know:
- The Meteo-France weather service warned of winds of up to 260 kilometres per hour (162 miles per hour) and waves as high as 15 metres (50 feet).
Vatomandry. Madagascar braced up for Cyclone Batsirai set to hit the eastern parts of the Indian Ocean island on Saturday, with powerful winds and torrential rains posing a "very serious threat" to millions.
Residents hunkered down before the storm makes landfall in a country still recovering from the deadly Tropical Storm Ana in late January.
The Meteo-France weather service warned of winds of up to 260 kilometres per hour (162 miles per hour) and waves as high as 15 metres (50 feet).
It said Batsirai would likely make landfall Saturday afternoon as an intense tropical cyclone, "presenting a very serious threat to the area" after passing Mauritius and drenching the French island of La Reunion for two days with torrential rain.
Residents in the eastern coastal town of Vatomandry were stockpiling supplies in preparation for the storm.
"We have been stocking up for a week, rice but also grains because with the electricity cuts we can not keep meat or fish," said Odette Nirina, 65, a hotelier in the seafront town of Vatomandry.
"I have also stocked up on coal. Here we are used to cyclones," she told AFP.
Gusts of winds of more than 50km/h were pummelling Vatomandry town Saturday morning accompanied by intermittent rain.
Residents have reinforced corrugated iron roofs with sandbags.
- 'We are very nervous' -
The United Nations said it was ramping up its preparedness with aid agencies, placing rescue aircraft on standby and stockpiling humanitarian supplies.
The impact of Batsirai on Madagascar is expected to be "considerable", Jens Laerke, spokesman for the UN's humanitarian organisation OCHA, told reporters in Geneva Friday.
At least 131,000 people were affected by Ana across Madagascar in late January. At least 58 people were killed, mostly in the capital Antananarivo. The storm also hit Malawi, Mozambique and Zimbabwe, causing dozens of deaths.
The UN's World Food Programme (WFP) pointed to estimates from national authorities that some 595,000 people could risk being directly affected by Batsirai, 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.
Search and rescue teams on the island have been placed on alert and residents reinforced their homes.
Inland in Ampasipotsy Gare, sitting on top of his house, Tsarafidy Ben Ali, a 23-year-old coal seller, held down corrugated iron sheets on the roof with large bags filled with soil.
"The gusts of wind are going to be very strong. That's why we're reinforcing the roofs," he told AFP.
The storm poses a risk to at least 4.4 million people in one way or another, the International Federation of Red Cross and Red Crescent Societies said.