The number of people seeking medical treatment for poisoning from toxic waste has risen from 10,000 to 16,000, say health officials in Ivory Coast.
The dumping provoked fury among Abidjan residents
Residents of the biggest city, Abidjan, have been reporting health problems, including headaches and vomiting, since a ship offloaded tons of waste.
These were dumped by a local company in leaking drums on open-air sites.
Four of the six dead are children. Last week the entire government resigned over the pollution scandal.
The UN has set up an inter-agency team and the Ivorians have recruited extra medical staff to deal with the crisis.
"There were a total of 15,749 consultations by yesterday evening," health ministry spokesman Simeon N'Da told AFP news agency.
"Of these, 23 people have been hospitalised and six have died."
A French team is analysing the waste and says it will produce a report by the end of this week.
The waste came from the ship, the Probo Koala, and has been found in at least 11 open-air sites around Abidjan.
Residents have been complaining of a smell of rotten eggs on the streets. Environmental group Greenpeace say the sludge dumped is made up of some 400 metric tons of oil-refining waste.
The company which owns the ship, Trafigura Beheer BV, says it is extremely concerned and has sent oil and mining experts to Abidjan to help the authorities.
It says it informed the authorities and handed over discharges from washing out its oil tanks with caustic soda - known as slops - to a certified local company, Compagnie Tommy.
A UN agency said that many of the sites where dumping occurred have still to be fenced off.