COLOMBO: The worst-ever outbreak of dengue fever has killed nearly 300 people in Sri Lanka, with aid agencies warning against further spread of the mosquito-borne viral disease.

The Sri Lanka Red Cross Society and the International Federation of Red Cross and Red Crescent Societies said that they were scaling up emergency assistance to the island nation, as the number of dengue cases topped 100 000.

"Dengue patients are streaming into overcrowded hospitals that are stretched beyond capacity and struggling to cope, particularly in the country's hardest hit western province," Red Cross/Red Crescent said in a statement.

The Red Cross announced it was increasing its budget by $300 000 to cope with the unprecedented outbreak.

The ministry of health said the number of dengue infections has climbed above 100 000 since the start of 2017, with 296 deaths.

That figure is nearly double the previous year, with about half those cases reported from the island's west, including the capital Colombo.

Health officials blamed the current crisis on recent monsoon rains and floods that have left pools of stagnant water and rotting rain-soaked trash, ideal breeding sites for mosquitoes that carry the virus - which causes flu-like symptoms and can develop into the deadly hemorrhagic dengue fever.

The Red Cross warned that ongoing downpours and worsening sanitation conditions raise concerns that the disease will continue to spread.