The largest school system in Kentucky closed schools Thursday and Friday following what the superintendent called a "transportation disaster" that left some children on buses until just before 10 p.m. Wednesday, the first day of school.

In a video statement posted to social media Thursday, Jefferson County Public Schools Superintendent Marty Pollio apologized to the district's 96,000 students, their families, bus drivers and school officials. He said that canceling day two and day three of school was the hardest decision of his superintendent career. The district, which includes Louisville, has 65,000 bus riders, according to its website.

"I saw some incredible instruction. Kids excited, families excited, new school buildings, and to have it end with the transportation disaster that we had last night was truly unacceptable. And once again, I apologize for that," he said in the video post.

In a Facebook post Wednesday, Pollio said JCPS "always experiences delays in transportation during the first days of school" but that what occurred Wednesday "is unacceptable."

"We acknowledge that the delays and frustrations felt by families were worse than in years past as bus drivers, families, students and school staff all worked to navigate a brand new transportation plan," he said in the statement.

Families waited for hours, according to the statement, for their children to return home after dismissal, and that as of 9:58 p.m. Wednesday, bus riders had not been dropped off.

"We will be working diligently to make adjustments with the goal of reducing bus wait times and ensuring every child who needs one has a safe ride to and from school," Pollio said in the statement.

Because children were delayed getting home to families, the Louisville Metro Police Department told CNN they had a few calls from parents. The children, however, were found prior to the report-taking process.

AlphaRoute, an engineering firm that develops transportation solutions and is under contract with JCPS, said in a statement to CNN that the company is working "diligently to resolve the issues it experienced," and it is not clear what the "full range of root causes were for those issues."

"But we recognize that the situation was extremely regrettable and likely caused by the significant changes to bus routing which were made necessary by the district's severe driver shortage," the statement said.

A "substantial amount of change" was caused by a new school assignment model, according to the statement. "We are fully confident that the new bell times and the new routes will work as planned, and we will do everything we can to support the district during this process."

In a Facebook post Wednesday, Teamsters Local Union 783, which represents some of the bus drivers in the district, said the first day of school was "a very difficult day for our School Bus Drivers at JCPS."

"We are very proud of our Members who went above and beyond to make sure every child was delivered home safely, even though the delivery times and conditions are 100% unacceptable," the statement said.

The issue could have been prevented "with allowing those who perform the task to sit at the table and help design the routes, give ample time to practice the routes, to ensure they are correct and to make sure the children do not suffer," the statement said. "This did not happen."

Officials will be working "around the clock" over the next several days to "work extremely hard to fix the errors that are in the transportation system," Pollio said in his video statement. "But I have to make sure our kids are safe and we will not have a repeat of what happened and we will not be in school until I know we can get kids home safely."

Pollio said officials will be reviewing bus routes and stops, and they plan to pay bus drivers extra days to practice new routes.