WASHINGTON, April 18 (Xinhua) -- Puerto Rico suffered from an island-wide blackout on Wednesday, nearly seven months after Hurricane Maria devastated the U.S. island's power grid.

The Puerto Rico Electric Power Authority (PREPA) said in a statement that a 230Kv power line suffered a failure "in one of its phases," and that it expects to restore electricity to nearly 1.5 million affected customers gradually in between 24 to 36 hours.

Hospitals, San Juan's airport, pumping systems and banking centers are the PREPA's top priority, while industries, shops and residences follows, the statement said.

The blackout prompted a outcry of criticism. San Juan mayor lamented that the failure brought the island back to Sept. 20, 2017, after Hurricane Maria wiped out the island's electric infrastructure, and U.S. Senate Minority Leader Chuck Schumer tweeted that the loss of power was "unacceptable."

The incident marks the latest setback for the island territory in its recovery after Hurricane Maria caused at least 48 deaths as well as widespread flooding. Less than a week ago, a fallen tree knocked out power for 870,000 customers on the Caribbean island.