Storm-battered Puerto Rico, with a population of 3.4 million, is still without electricity five days after Hurricane Maria struck with ferocious winds and torrential rains, the most powerful hurricane to hit the US territory for nearly a century.

There have been growing concerns for some 70,000 people who live in the river valley below the Guajataca Dam in the island’s northwest, where cracks were seen, on Friday, in the 88-year-old earthen structure.

The National Weather Service warned of further flash floods in the west of the island on Monday as thunderstorms moved in.