Half a million people have already been affected by the floods
Namibian human rights activists have accused the government of failing to prepare for heavy flooding that has swamped southern Africa.
The head of the National Society for Human Rights (NSHR), Phil ya Nangoloh, told the BBC that people had been left without food or shelter.
He said diseases such as cholera and malaria were spreading.
Namibia's government said the waters were receding but areas in the north were still not accessible by road.
An area 1,500km (930 miles) wide, from Namibia in the west to Mozambique faces rising waters from several rivers.
On Tuesday, the International Federation of Red Cross said the floods had claimed at least 120 lives and affected half a million people.
"They are always caught pants down by this flooding. There have been indications from weather people that another flooding is coming," Mr Nangoloh told the BBC's Network Africa programme.
"Our prime minister in January stated through one of the newspapers that the government is not prepared, the emergency units are not prepared," he added.
"They are under-funded they are under-stocked. The blames goes to the government in short."
He said they had advised the government last year to put in place a drainage system in areas most vulnerable to flooding but had received no response.
But Francis Kooper, deputy director of the emergency response unit in prime minister's office, said that despite annual flooding in Namibia they could not have predicted such serious inundation.
"That experience is new it's only coming from last year, some people are saying that in 52 years they never experienced this kind of flood," he told the BBC.
"We never experienced in the past heavy rainfalls, the torrential type of rainfall, it has never been the case."
The Red Cross says it has only managed to reach a small fraction of those affected.
It has appealed for helicopters and boats to reach isolated communities.
The organisation expects the flood waters to remain for at least the next four to eight weeks.
Some of the floodwaters have reached densely-populated areas - up to 30km (19 miles) from the Zambezi river - that communities say have never been affected by flooding before.