SAN JUAN, Puerto Rico — The administrator of the U.S. Federal Emergency Management Agency said Friday it will take up to an estimated $50 billion to help rebuild Puerto Rico from Hurricane Maria and warned that the U.S. territory is not ready for another disaster.

Brock Long said his agency aims to make the island’s roads, homes, bridges and electrical grid as strong as possible but noted that the next hurricane season starts June 1.

“We’re running out of time,” he said during a visit to Puerto Rico, adding that much of the island’s infrastructure collapsed. “We have a long way to go.”

Long said his agency also is coordinating a June 14 planning and training exercise with Puerto Rico’s government in which life-saving supplies will be delivered to the island’s 78 municipalities to ensure better response times for any upcoming storms. Cities and towns will be allowed to store those supplies.

FEMA and local government officials have stockpiled more than 15.6 million liters of water and more than 2.8 million meals in five warehouses across the island in the event of another disaster. Long stressed that Puerto Rico’s public and private sectors have to build a strong emergency response network and establish unified plans.

He also said the private sector should ensure that communication systems become more resistant. Maria left nearly all of Puerto Rico without phone service after the storm hit Sept. 20.

Mike Byrne, FEMA’s federal coordinating officer in Puerto Rico, said he is working with the U.S. territory’s government to determine how federal funds will be used to identify priorities and rebuild damaged infrastructure.

Byrne said some of the money will go toward strengthening the island’s power grid since the storm destroyed two-thirds of its distribution system.

More than 50,000 power customers remain in the dark, but he said 96 percent of all customers now have electricity.

On Thursday, Puerto Rico’s Department of Education announced it will close 283 schools this summer after a sharp drop in enrollment amid the island’s long economic slump and the continued departure of families after Maria.

Education Secretary Julia Keleher said there would be no layoffs, with teachers and other employees being reassigned to other schools as part of a plan that aims to save the department $150 million.

Puerto Rico has more than 1,100 public schools serving 319,000 students.