CORVALLIS, Ore. (AP) — Oregon State University officials have given the go-ahead to people on campus to resume activities after warning them on Tuesday not to open any food delivery robots because of a bomb threat.

University officials at the Corvallis, Oregon, campus at lunchtime sent out what they called an urgent alert on X, formerly known as Twitter, that there was a bomb threat in Starship food delivery robots.

“Do not open robots,” the post said. “Avoid all robots until further notice.”

The post said campus public safety officials were responding.

The university said about an hour later that the robots had been isolated in a safe location and that technicians were investigating. About 15 minutes after that, officials said on X that the emergency was over.

“All Clear,” the post said. “You may now resume normal activities. Robot inspection continues in a safe location.”

San Francisco-based Starship Technologies, which makes the robots, said in an email Tuesday afternoon that a student at the Oregon State University sent a bomb threat through social media that involved the campus robots.

The student has since said it was a joke and a prank, the company said, but added that it has suspended the service while it cooperates with the investigation.

The university is actively investigating the bomb threat, university officials said in an email Tuesday afternoon.

“The OSU Department of Public Safety is following protocols for this evolving situation to protect the safety and security of OSU’s students, staff and visitors, which is our top priority,” Rob Odom, Oregon State University vice president of university relations and marketing, said.

A spokesperson for the Corvallis Police Department said their department is not involved in the investigation.

About 20 small Starship delivery robots began bringing food orders to students, staff, and faculty, in 2020, KOIN-TV reported.

“You unlock it, get your food and then off it goes to get sanitized and prepare for another delivery,” Kerry Paterson, director of OSU’s residential dining and university catering, told the news outlet at the time.

San Francisco-based Starship Technologies said on X earlier this month that the robots had rolled onto nearly 50 college campuses in the U.S., serving over 1 million students.