BAYAMÓN, Puerto Rico (AP) — A power company in Puerto Rico announced Thursday that it has restored electricity to most areas affected by a massive outage that hit the U.S. territory the previous day.

The outage left over 340,000 customers in the capital, San Juan, and neighboring municipalities without power during a heat wave. On Thursday morning, Luma Energy said in a statement that it had restored power to most of its customers in the metropolitan and northeastern regions of the island. The company also confirmed that the outage stemmed from failures in two transmission lines between San Juan and Aguas Buenas.

Several lawmakers in Puerto Rico are urging the governor to declare a state of emergency to the federal government. Persistent outages have interrupted water service and imperiled the lives of elderly and ill residents who rely on electrical equipment for respirators and to refrigerate insulin, for example.

Electricity supply problems occurred for over a week in the island’s southern region, and culminated in the massive outage on Wednesday night.

“This is really dangerous,” said Jenniffer González, Puerto Rico’s representative in the U.S. Congress. “At the federal level, what I’m suggesting is that Puerto Rico declare itself in an energy emergency situation so that any procedure with federal agencies can be expedited.”

González said that would also enable personnel from the U.S. Department of Energy, the Environmental Protection Agency and the Federal Emergency Management Agency to provide assistance. Several mayors echoed her request.

About 5,000 customers across the island were still without power as of Thursday morning, while several municipalities on the eastern side of Puerto Rico lacked water. The University of Puerto Rico in San Juan canceled its summer session classes on Thursday.

“The situation we have experienced for weeks on the island is unsustainable,” said Gabriel Hernández Rodríguez, President of the Puerto Rico Mayors Federation. “The impact on the economy and the daily lives of citizens and business owners due to the lack of electrical power generation and transmission is terrible, causing losses and complications.”

Several unions are denouncing Luma Energy and Genera PR, the two main companies in charge of transmission and generation on the island, and are calling for the government to cancel its contract with Luma Energy.

“Due to constant power outages, thousands of citizens have lost electrical appliances in their homes, thrown away groceries, patients have stopped receiving their treatments, our schools have become ovens in the heatwave, our classroom equipment is getting damaged, and our students and teachers arrive sleepless to the classroom, negatively impacting teaching and learning conditions,” the Teachers’ Federation of Puerto Rico said in a statement.