Conestoga High School in Chester County opened with a three-hour delay on Thursday after someone called in a bomb threat, the Tredyffrin/Easttown School District said.

Tredyffrin Township police were called to the school before 6 a.m. after the 911 Call Center received the threat and sent officers and a K-9 unit to the school. The K-9 unit was deployed to search the school building, police said in a Facebook post.

Before 9:30 a.m., police posted on Facebook that the school had been cleared and no threat was found.

"Authorities have determined the threat was a hoax, and the building has been cleared for students and staff to return. While the caller has not been identified, the matter remains under investigation," administrators said in a post on the school website.

The school district said the delay was out of an abundance of caution and to give police time to clear any threat. All other district schools will open on their regular schedules.

Conestoga initially had a two-hour delay, but extended it to three hours later in the morning.