Haiti was counting the cost of the devastation wrought by Hurricane Matthew on Saturday night, with almost 900 inhabitants killed and tens of thousands displaced in the Caribbean country.

Outbreaks of cholera led to the deaths of several people, because of flood water mixing with sewage, and fears were growing that the disease could spread.

“Due to massive flooding and its impact on water and sanitation infrastructure, cholera cases are expected to surge after Hurricane Matthew and through the normal rainy season, until the start of 2017,” the Pan American Health Organisation said in a statement.

Matthew rampaged through Haiti’s western peninsula on Tuesday with 145mph (233km/h) winds and torrential rain. Some 61,500 people remain in shelters, according to officials who said that the storm had hit fragile coastal villages, some of which were only now being contacted.

One of Haiti’s most acutely affected regions centres on the beach town of Port-Salut, on the south-western peninsula of the country. At least three towns in the hills and coast of Haiti’s fertile western tip reported dozens of people killed. These included the farming village of Chantal, where the mayor reported that 86 people had died, mostly when trees crushed houses.

“A tree fell on the house and flattened it. The entire house fell on us. I couldn’t get out,” said 27-year-old driver Jean-Pierre Jean-Donald.

“People came to lift the rubble, and then we saw my wife, who had died in the same spot,” said Jean-Donald, who had been married for only a year. Fears the storm would cause similar damage on the US mainland proved unfounded as the hurricane steadily weakened throughout Saturday, although five deaths were reported – three in North Carolina and two in Georgia.

There was a period early on Saturday when Matthew – the most powerful hurricane to threaten the Atlantic seaboard in more than a decade – had prompted significant disquiet with mass evacuations in four US states and power failures affecting more than 1.6m homes and businesses.

Throughout Saturday , the hurricane gradually lost strength as it moved north parallel to Florida’s coast, with winds reaching up to 120mph (195km/h) but staying just far enough offshore to ensure coastal communities escaped the full force of its winds. Florida’s governor, Rick Scott, expressed his relief that the hurricane had stayed offshore, saying its impact would have been far worse. He said he hoped power would be restored throughout the state by late on Sunday.

Accounts from the peninsula documented how the storm swamped streets, gouged out roads, toppled trees and left an estimated 1 million people without power in Florida alone. The hurricane also brought some of the highest tides on record to the South Carolina coast, flooding the streets and intersections in historic Charleston, a city of pre-civil war homes, church steeples and romantic carriage rides.

Of the reported fatalities, two people in Florida were killed by falling trees and an elderly couple died of carbon monoxide poisoning inhaled from a generator while sheltering from the storm inside a garage.

By Saturday afternoon, the US National Hurricane Centre had downgraded Matthew to a Category One hurricane, as maximum sustained winds decreased to 75mph.

The governor of South Carolina, Nikki Haley, warned people to stay in shelters and not to try to go back home, and she appealed for patience.

“It’s still a very serious situation, and we are not out of the woods,” she said. “Now is when the frustration sets in. Most injuries, most fatalities happen after the storm … we want to make it safe for you to find out about your home.”

President Barack Obama, along with federal and local officials, urged people not to be complacent and to heed safety instructions. Coastal residents have been warned that storm surges could still pose a danger by flooding entire neighbourhoods, even as Matthew departs the region.