The hours-long storm triggered flash floods that inundated streets and damaged infrastructure in the capital Luanda and the southern city of Benguela on the country's Atlantic coast.

Benguela bore the brunt of the devastation, with 12 deaths reported there and three in Luanda, the fire service said, citing a preliminary report.

"I've lost almost everything and I don't know where to go," said Natalia, a resident of Luanda's poor Kilamba neighbourhood, describing how her home was turned into a "swimming pool" by the floods.

Her family had moved their children and grandchildren to stay with relatives, she told AFP.

"We really are at a loss for words. May God help us."

Heavy downpours are not unusual in the southwest African country during the rainy season, but scientists say human-caused climate change is increasing the probability, length and severity of such extreme weather events.

In neighbouring Namibia, the Zambezi River has risen sharply, forcing thousands of people living along its banks to flee their homes.

Officials said water levels had reached about 6.8 metres (22 feet), well above the usual four metres.

Authorities have relocated residents to nine temporary camps, including one sheltering more than 2,700 people, officials told AFP on Saturday.