Prince George’s County authorities investigate a bomb threat at Six Flags America in Upper Marlboro, Md. (Prince George’s County Fire Dept.)

Authorities in Prince George’s County said a bomb threat at Six Flags America that closed the amusement park Wednesday is now over.

They responded to the park in Upper Marlboro early Wednesday after a park supervisor received a text message about bombs at Six Flags, a spokesman for the Prince George’s Fire Department said.

Security personnel deployed around the park and found two unattended backpacks that were determined not to be explosive. The all-clear was announced after a search of the park around 2:45 p.m., the spokesman said. Six Flags announced that the park would be open until 8 p.m.

The spokesman said the incident remained under investigation.