Africa's harbour cities of Cape Town, Lagos and Alexandria are under threat from rising sea levels which could displace millions and cause massive economic losses, scientists said Wednesday.

Speaking at an international climate change conference in Cape Town, Geoff Brundrit of the Global Ocean Observing System in Africa said even a slight increase in sea levels could wreak havoc on some countries.

"Disaster risk is high when the chance of occurrence of a hazard is high, when the vulnerability to damage from that hazard is high and when the capacity to cope with the consequences of the occurrence is low," he said.

Brundrit told AFP that many African countries had "no resilience" to increasingly damaging storms as a result of the changing climate, and were often hit by the next before properly recovering from the last.

This, he said, made countries on the continent extremely vulnerable.

Lagos, in Nigeria, is Africa's most densely populated city with a population of more than 15 million people living between a lake and the sea.

With people crammed into every available space often right up to the shoreline, storms already flood low-lying streets. Rising sea levels could swallow tracts of land, Brundrit said.

"Where will the people go?" said Brundrit, who said the state government was "more concerned with the development of Lagos" than with managing the risks.

According to Brundrit, "adaptation through protection will be difficult and expensive" across Africa's coast and immediate assessment needs to be done and policies put in place.

"If you are really going to take cognisance of sea-level rise, put buffer zones along the coast where you restrict development," he said.