Papua New Guinea's cholera outbreak has spread to 2,000 people, a World Health Organization official said Monday as he warned that poor water sanitation was making the disease hard to contain.

The country's first cholera outbreak in 50 years emerged in northern Morobe province last July and within months had spread along the north coast to Madang and East Sepik, WHO representative Eigil Sorensen said.

"We have seen the ongoing transmission in all these three provinces at the moment so it is gradually spreading," Sorensen told AFP.

"We have now more than 2,000 confirmed cases of cholera."

Sorensen said the number of deaths so far remained modest at fewer than 50, but the disease continued to spread due to poor water supplies and as infected people, including those with no symptoms of the sickness, travelled around.

Sorensen said many areas of Papua New Guinea, particularly crowded settlements on the outskirts of cities with no proper sewage systems, provided the ideal conditions for the spread of cholera.

"We feel that from a public health perspective it is very important to address the water issue," Sorensen said.

"The government needs to do more. Otherwise there is the risk that cholera spreads to other provinces and becomes endemic in Papua New Guinea."

Cholera, a water-borne disease which can also be transmitted by food that has been in contact with sewage, causes serious diarrhoea and vomiting leading to dehydration. It can be fatal if not treated in time.