Ernesto becomes hurricane after leaving 728,000 without power in Puerto Rico

Ernesto has become a Category 1 hurricane Wednesday after hitting Puerto Rico overnight and leaving power outages and flooding in its wake.

The center of then-Tropical Storm Ernesto passed within 40 miles of San Juan, Puerto Rico , early Wednesday, producing strong winds and heavy rain.

More than 728,000 customers are without power in Puerto Rico, just shy of half the island, according to LUMA, a service provider. The island's eastern and central regions are the most impacted.

LUMA said only power lines are down, not the infrastructure that delivers power. It will need 24 to 48 hours to assess damage before providing any time frame for repairing the lines.

The primary cause of the outages were high winds, which have been recorded at speeds of 50 mph or more, according to Juan Saca, the president and CEO of LUMA Energy.

"In Puerto Rico, vegetation under the power lines is a major issue. The movement of trees between the lines can easily cause outages," Saca said.

Despite the challenges, Saca said LUMA is better prepared than ever to restore power.

Additionally, 235,000 customers are without water and over 400 people are in shelters, according to Puerto Rican officials.

Officials are asking people to leave their homes only if absolutely necessary. Many villages are completely isolated because of the river levels and multiple routes are closed.

Officials asked people to donate blood due to low resources. Twenty-three hospitals are using electric generators and 80 flights have been canceled.

The highest rainfall total recorded Wednesday midday was 9.6 inches in Naguabo, Puerto Rico.

All tropical storm warnings have been canceled for Puerto Rico and the Caribbean islands, but flash flooding still remains a concern in Puerto Rico due to heavy rain. Rain was ending late Wednesday afternoon.

A hurricane watch has now been issued for Bermuda.

On Culebra island, east of Puerto Rico, sustained winds of 68 mph were reported with a gust up to 86 mph. A METAR Observation Station at the Roosevelt Roads Naval Station in Puerto Rico reported sustained winds of 48 mph and a gust of 74 mph.

On the forecast track, Ernesto will continue to strengthen Thursday into Friday. It may become a Category 3 hurricane by Friday morning with winds up to 115 mph.

Friday night into early Saturday, Ernesto will be making its approach to Bermuda as either a low-end Category 3 hurricane or high-end Category 2 hurricane. Wind and rain is expected there.

The East Coast will see high surf and rip currents through this weekend as Ernesto moves parallel, but well away from, the coast.

President Joe Biden approved an emergency declaration for Puerto Rico on Tuesday night.

Puerto Rico Gov. Pedro Pierluisi had warned residents to stay home starting on Tuesday evening, when the tropical storm-force winds are forecast to reach the island. Total rainfall could reach up to 10 inches in some spots.

ABC News' Jessica Gorman and Josh Hoyos contributed to this report.