HILO » A small bomb exploded Thursday outside an auditorium at Hilo High School, prompting a brief campus lockdown but apparently causing no injuries, authorities said.

Police said two students, both 16-year-old boys, were in custody. It wasn’t clear whether the device was meant to hurt anyone or if it was a prank.

The small device exploded at about 11:15 a.m. and was described as a "bottle bomb," state Department of Education spokes­man Alex Da Silva said.

It went off on a walkway leading to the auditorium, he said. A class was in session in the auditorium, but nobody was near the explosion.

Nobody was allowed to leave or enter the campus during the lockdown, but police and fire officials gave an all-clear less than two hours later after finding no other devices on campus, Da Silva said. Classes resumed, and students were released at the normal time.

"Police recovered the remnants of a plastic liquid container and unidentified liquid substance," police said in a news release.

"I heard a boom, then they said stay in our classroom and we couldn’t leave," said 14-year-old freshman Erika Taga­li­cot. "There was a lot of cops and fire guys here."

Tagalicot said that despite the incident, she will not be nervous to go back to school today.

Debra Palisbo, a 14-year-old freshman, said she didn’t hear the explosion, but was in computer class when one of her classmates got up and walked outside. "I saw a cop put him in the car," she said.

PTSA President Karen Tollestrup said her daughter texted her that there was a lockdown because of an explosion but that she was safe. Tollestrup also received two automated phone calls — one saying there was a lockdown and then another one saying it was lifted.

"I’m always concerned when there’s a lockdown," she said. "It is Hilo so I wasn’t totally concerned. But in the news lately there have been so many incidents on the mainland."

Roosevelt High School in Hono­lulu was locked down Tuesday when an officer shot a knife-wielding teen in the wrist.

"It was because of Roosevelt I thought, ‘Gosh, what if someone shot someone?’ But Hilo is a pretty safe town," she said.

That’s why she would have liked to have known exactly what happened.

"The thing I was most concerned about is I didn’t know why they were in lockdown. I guess I would have like to (know) at the time why (they) were in lockdown," she said. "But I wasn’t concerned to the point I was nervous."

The principal didn’t immediately respond to requests for comment.