All public schools in Trumbull were closed Monday because of what the district called a “massive bus failure,” according to a message on its website.

An email sent to families by Superintendent Martin Semmel and obtained by News 12 said that because of the cold weather, diesel buses were experiencing fuel gelling.

While many buses started normally at the garage, the fuel began to harden on the road, causing them to break down.

At first, Semmel said it was only a few buses, but as the morning went on, it began happening to most of them. The bus company ultimately recommended closing all schools.

That announcement was made in an email at 7:35 a.m.—the same time Trumbull Middle School starts its day, and 10 minutes after Trumbull High School’s first bell.

Michael Greco, a freshman at Trumbull High, said he had already arrived at school when students started getting the news on their phones. “My teacher didn’t believe it, but then they announced it on the PA system. Our principal seemed a little confused too,” Greco said. “I heard everybody cheering, but I was a little upset because it was horrible to get to school and have to leave right away—I had to get ready, wake up early, everything.”

In the email, Semmel said staff members remained at the buildings to ensure students were supervised until they had a way home.

The bus company tells News 12 that it investigated the issue, and bus service will resume on Tuesday.