Dengue cases have created an "emergency situation" in the Americas, although cases in hotspots Argentina and Brazil appear to have stabilized, the head of the Pan American Health Organization (PAHO) said on Thursday.

PAHO, a United Nations agency, has confirmed more than 5.2 million cases of dengue across the Americas this year, an over 48% jump from the 3.5 million cases the group reported late last month.

More than 1,800 people have died from the mosquito-borne viral illness, up from over 1,000 deaths reported last month in the year through March.

"We have an emergency situation," PAHO Director Jarbas Barbosa said in a press briefing.

The countries so far hit the hardest in the current outbreak, Argentina and Brazil, "still have a very strong transmission," Barbosa said, adding that "in recent weeks there seems to be a stabilization, or even a reduction" in the countries' cases.

Barbosa warned that supply of an existing dengue vaccine is "very limited" and even widespread vaccination would not have an immediate impact on interrupting the ongoing outbreak.

"The dengue vaccine can play an important role in reducing severe cases of deaths, but it will take time until the effects of the vaccine can be reflected in the decrease in dengue cases," Barbosa said.

Dengue symptoms include fever, headaches, vomiting, skin rashes, as well as muscle and joint pain. In some cases, it can cause a more severe hemorrhagic fever, resulting in bleeding that can lead to death.