SAN JUAN, Puerto Rico — All people living near the Guajataca River in northwest Puerto Rico should evacuate immediately because of an “imminent dam break,” the National Weather Service in San Juan said Friday afternoon.

“All Areas surrounding the Guajataca River should evacuate NOW. Their lives are in DANGER! Please SHARE!” an earlier tweet said.

About 70,000 people in the area of the Guajataca Dam have been told to evacuate, National Guard spokeswoman Yennifer Alvarez told CNN’s Leyla Santiago. Buses have been brought in to help people leave.

Puerto Rico Gov. Ricardo Rossello said on Saturday afternoon that the dam was holding up, but residents should still evacuate the area until further notice.

“We don’t know how much longer it will hold,” said Rossello. “The structure has been significantly compromised.”

Due to damaged telephone lines and lack of radio contact, Rossello said authorities have to physically go to the area and alert residents of the dangers posed by a possible dam breach.

Speaking on CNN’s “Out Front” with Erin Burnett, Puerto Rican Secretary of State Luis Gerardo Rivera Marín said the evacuations are difficult because the island was heavily damaged by Hurricane Maria, which struck earlier this week. Many parts of Puerto Rico are flooded and more than 3 million people don’t have electricity.

“It is (done) in the blackness of the night,” he said. “There’s lack of energy, especially in the mountain regions where the winds were higher speeds.”

The NWS issued a flash-flood notice for the towns of Isabela and Quebradillas, which are about 6 miles apart. Isabela has about 45,000 people, Quebradillas 25,000 people.

The dam was constructed by the Puerto Rico Electric Power Authority to create a lake that provides drinking water to residents of the area, according to the US Geological Survey..