At least eight people were killed after flooding on Cape Verde's Sao Vicente island overwhelmed emergency services and cut key roads, a regional civil protection councillor said on Tuesday.

On Monday morning torrential rains lashed the northern island in the Atlantic archipelago located off West Africa, swamping roads and sweeping away vehicles and people.

Municipal councillor Jose Carlos da Luz told a state broadcaster seven people had died in floods and one person was electrocuted, adding that three others were still missing.

In a report on Monday, the International Federation of Red Cross and Red Crescent Societies put the death toll at nine and said 1,500 people had been displaced on Sao Vicente.

'Rare situation'

Sao Vicente usually records 116 millimetres (mm) of rain in a year, according to Cape Verde's meteorology institute. But early on Monday, 193 mm fell in just five hours, according to Ester Brito, an executive at the institute.

"It is a rare situation because what was recorded is above our 30-year climatological average," she told Reuters, adding that in just two hours more rain fell than the island typically receives annually.

The US National Hurricane Center said on Monday that Tropical Storm Erin was located about 455 kilometres west-northwest of Cape Verde and packing maximum sustained winds of 75 km/h.

Interior Minister Palo Rocha said on Monday that floodwaters disrupted transport across Sao Vicente and severed the main road to Cesaria Evora International Airport, though the facility remained operational. Rockfalls also blocked traffic.

'Difficult night'

"It was a difficult night marked by panic and despair," Rocha told public radio, adding that first responders were inundated with distress calls.

Rescue and cleanup operations were ongoing, but Rocha said authorities were mobilising resources that would allow the island to quickly return to normal life.