“What’s happening must be taken seriously, very seriously even,” the Indian Ocean department’s central government representative Jerome Filippini told a press conference.

He said the island’s 870,000 residents must “have stocks of water and food, and be prepared to live autonomously for several hours or several days, and have a first-aid kit”.

The storm, dubbed Belal, could hammer the island with winds of up to 150 km/h (90 mph) if it only passes nearby, according to the Meteo France weather service.

But “a direct hit cannot be ruled out, which would imply winds of more than 220 km/h on the coasts and 250 km/h in the highlands”, Meteo France’s regional director Celine Jauffret said.

An ocean storm surge of six metres (20 feet) and heavy rain is also expected.

“I took just one six-bottle pack of water, I had already stocked up before,” said Aurore Fontaine, an accountant among throngs of shoppers at a supermarket in the main city of Saint-Denis.

“I also bought canned food and some deli meats for making sandwiches.”

On the west of the island, Jean-Pierre Mondon said his water tank was full, but he was more worried about his tomato and lettuce crops. “I was going to harvest them in just a week, but now it’s ruined,” he said while taking down his protective greenhouses. “It’s better to do it before the wind blows it all away.

The last major cyclone to hit Reunion was in 2014.