An explosive outbreak of polio is taking place in the Congo Republic, with 201 cases of paralysis found in two weeks and 104 deaths, the World Health Organization said Tuesday.

The government in Brazzaville, the nation’s capital, has declared an emergency and announced plans to vaccinate the entire population with oral drops three times with help from the W.H.O., Unicef and the United States Centers for Disease Control and Prevention.

In Pointe Noire, the port city where most of the cases are concentrated, “We’ve got two hospitals with hundreds of paralyzed people and many dead,” Dr. Bruce Aylward, the W.H.O.’s director of global polio eradication, said in an interview from Geneva. “And a couple of things about this outbreak are different and deeply disturbing.”

Polio normally strikes young boys and girls equally, killing no more than 20 percent of those it paralyzes; death ensues when paralysis moves up the spine to the nerves that control the breathing muscles. In Pointe Noire, 85 percent of the cases are in teenagers and adults, most victims are male, and the death rate is much higher.