Matthew, swirling off the northern coast of Colombia and Venezuela and forecast to head towards Jamaica and Cuba, was packing winds of 160 miles (260 kilometers) per hour, making it the strongest storm on the NHC's 1-5 scale, the NHC said in its 0300 GMT bulletin.
The storm is also the most powerful since Hurricane Felix in 2007, the Miami-based monitor said.
The center of Matthew was located 80 miles (125 kilometers) northwest of Punta Gallinas, Colombia, and 440 miles southeast of Kingston Jamaica.
Jamaica and southern Haiti were preparing for heavy rain and flooding as the storm headed in their direction and forecasters said 10-15 inches (25-38 centimeters) of rain could fall across the region.
"These rains may produce life-threatening flash flooding and mud slides," the NHC warned, saying isolated areas could be lashed with up to 25 inches of rain.
"Some fluctuations in intensity are possible this weekend, but Matthew is expected to remain a powerful hurricane through Sunday," the Center added.
"We invite them to secure the area surrounding their homes and begin to stock up on water and food," Edgar Celestin, a spokesman for the Haitian civil protection agency, told AFP.
Haiti was expecting the largest rainfall and wind gusts to come Saturday and Sunday.
Matthew became a Category 1 hurricane on Thursday afternoon, then swiftly rose to Category 4 a day later.
Ocean swells with the potential to cause dangerous currents and rip tides are also possible over the next two days in coastal regions of Puerto Rico, Venezuela, Aruba, Bonaire, Curacao, Colombia, the Dominican Republic and Haiti.
Hurricane Felix killed some 150 people and left thousands homeless when it slammed the Caribbean coast of Nicaragua in September 2007.