Arvada police on Thursday are investigating after a Postal Service mailbox was destroyed in a suspected early morning pipe bomb explosion.

The scene, near the intersection of 58th Avenue and Ralston Road, was discovered about 7 a.m.

“We have our lab out here,” said Jill McGranahan, a police spokeswoman. “We are out investigating it now.”

McGranahan said police received several 911 calls around 2:30 a.m. from residents in the area who heard a loud explosion. Responding officers found nothing and cleared the reports before the destroyed box was found about five hours later.

McGranahan said evidence found around the destroyed mailbox led authorities to believe the damage was caused by a pipe bomb.

Photos from the scene showed dozens of evidence markers spread out around the mangled remains of the mailbox.

The USPS has been notified, police say.

“This is still a very active investigation,” McGranahan said.

The box is near several business. No one was injured.

Jesse Paul: 303-954-1733, jpaul@denverpost.com or @JesseAPaul