An Upper East Side high school graduation was interrupted by a bomb threat Tuesday morning, police and witnesses said.

A representative at Vanguard High School, on East 67th Street near First Avenue, told police around 9:30 a.m. a caller said there were two pipe bombs inside the school that would detonate in 35 minutes, police said.

The graduation was approximately 30 minutes into the three-hour ceremony when the school’s principal, William Klann, approached the podium for an unexpected message.

“My principal made an announcement saying that everybody needed to evacuate,” said graduate Lucas Martinez, 19, who lives in Washington Heights. “There were cops at the front entrance … Nobody knew why at first.”

Dozens of graduates flooded the sidewalks, and the ceremony was relocated to nearby St. John Nepomucene R.C. Church.

Members of the NYPD’s Bomb Squad and Emergency Service Unit determined the building was clear of any bombs around 11 a.m.

“Interesting graduation day,” Martinez added.

A representative from the school could not immediately be reached for comment.