Puerto Rico opened just 20 percent of its public schools Tuesday after delaying opening nearly three weeks amid ongoing earthquakes that have rocked the island.

Only 177 schools were certified to open Tuesday after engineers inspected them for damage following the 6.4 magnitude earthquake on Jan. 7 that left one person dead and damaged hundreds of properties, The Associated Press reported.

However, the inspections were not tasked with determining whether a school could withstand another earthquake, according to the AP.

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Engineers have inspected 561 of the island’s 856 public schools. At least 50 were determined unsafe to reopen, with 240,000 students out of school.

Since the Jan. 7 earthquake, there have been several aftershocks across the island, including a 5.9 magnitude earthquake on Jan. 11 and a 5.0 magnitude quake that hit on Saturday. Engineers automatically have to re-inspect schools after any earthquake that is magnitude 3.0 or higher, according to the AP.

The initial earthquake leveled the top two floors of a three-story school in Guánica, the outlet reported.

Engineers say that 500 public schools in Puerto Rico were built prior to 1987 and fail to meet new construction codes. Officials said a plan to retrofit an estimated 756 buildings could cost up to $2.5 billion.

Gov. Wanda Vázquez Garced said Tuesday that her administration is trying to find alternative options for students who cannot return to schools. She said holding classes outside poses problems for educators, including how students will receive meals and access bathrooms and transportation.

Education Secretary Eligio Hernández said 51 schools are also scheduled to begin classes on Feb. 3, the AP reported.

“The Department of Education is going to take the time it needs and will take all necessary actions so that parents ... feel satisfied,” he told reporters on Monday, the AP reported.

Elba Aponte, president of Puerto Rico’s Association of Teachers, told the AP that she has received photos and complaints from parents and school employees who allege that at least 10 schools that have been reopened are unsafe for staff and students. The photos show mostly cracks in walls and roofs, the AP reported.

“It’s terrible,” she told the outlet. “If there was one place where they could feel safe, it was at school.”