"Months and months and months and months are going to pass before we can recover from this," Felix Delgado, mayor of the northern coastal city of Catano, told The Associated Press.
Videos posted on social media showed swift floodwaters and powerful winds brought to Puerto Rico by Maria.
Maria knocked out power to the entire island and its 3.4 million residents, officials said Wednesday.
Ricardo Ramos, CEO of the Puerto Rico Electric Power Authority, told CNN that it could be as long as six months before power is restored.
“The system has been basically destroyed,” he said.
Maria continued to churn over the Atlantic Ocean as a major Category 3 hurricane on Thursday afternoon with maximum sustained winds measured at 115 mph, the National Hurricane Center said in an 11 a.m. advisory. Officials warned that the storm, which is expected to turn to the north early Friday, could still strengthen over the next day or two.