SAN SALVADOR (Reuters) - Health authorities in El Salvador have declared an epidemic of dengue fever in five of the nation's 14 provinces and put the rest of the tiny country on red alert for the mosquito-borne disease.

The disease has killed six children under the age of 10 since January and spread to 595 people, including 102 with the more severe hemorrhagic strain, a Health Ministry spokesmen said on Saturday.

Health Minister Jose Lopez Beltran has warned that if it is not brought under control, dengue may kill up to 25 people by year's end, the spokesmen said.

The five provinces declared to have epidemic levels are San Salvador, La Paz and La Libertad in the center of the country and Sonsonate and Ahuachapan in the west.

Dengue fever, for which there is no vaccine, causes unbearable muscle and joint pains, high fevers and severe headaches. Its most potent form, hemorrhagic dengue, it can cause internal bleeding and death.

A 1995 epidemic of dengue fever killed five people.