Photo: The Canadian Press

Jennifer Lopez announces hurricane recovery efforts for Puerto Rico, Sunday.

Puerto Rico's nonvoting representative in the U.S. Congress said Sunday that Hurricane Maria's destruction has set the island back decades, even as authorities worked to assess the extent of the damage.

"The devastation in Puerto Rico has set us back nearly 20 to 30 years," said Puerto Rico Resident Commissioner Jenniffer Gonzalez. "I can't deny that the Puerto Rico of now is different from that of a week ago. The destruction of properties, of flattened structures, of families without homes, of debris everywhere. The island's greenery is gone."

Engineers on Sunday planned to inspect the roughly 90-year-old Guajataca Dam, which holds back a reservoir covering about five square kilometres in northwest Puerto Rico. The government said it suffered a large crack after Maria dumped nearly 40 centimetres of rain on the surrounding mountains and that it "will collapse at any minute." Nearby residents had been evacuated, but began returning to their homes Saturday after a spillway eased pressure on the dam.

Puerto Rico's National Guard diverted an oil tanker that broke free and threatened to crash into the southeast coast, said Gov. Ricardo Rossello, and officials still had not had communication with nine of 78 municipalities.

"This is a major disaster," he said. "We've had extensive damage. This is going to take some time."

The death toll from Maria in Puerto Rico was at least 10, including two police officers who drowned in floodwaters in the western town of Aguada. That number was expected to climb as officials from remote towns continued to check in with officials in San Juan. Authorities in the town of Vega Alta on the north coast said they had been unable to reach an entire neighbourhood called Fatima, and were particularly worried about residents of a nursing home.

Across the Caribbean, Maria had claimed at least 31 lives, including at least 15 on hard-hit Dominica.