The incident happened at about 4.20am on Sunday in Livingstone Street.

It was one of four explosions that woke hundreds of residents in the area. Police said letterboxes were also destroyed in Dent and Mitchell streets. An unexploded device was found at about 6.15am in a letterbox in Kilgour Avenue.

Brad Heath saw his letterbox blown to pieces from his bedroom window, which was broken in the blast.

"I saw a flash of light and then kaboom," said Mr Heath, of Livingstone Street.

"It was a very powerful blast - I thought it was a pipe bomb."

Police later told him a "big bundle of bungers" was used.

Moments before the blast at his place, Mr Heath let his cat in through the front door.

He heard the first two explosions, which he initially thought were thunder, before his letterbox blew up. He then heard a fourth blast.

The explosion in his letterbox caused a big cloud of smoke to drift up the road, rising above power lines.

As well as shattering his windows, the blast broke a piece of timber off the front of his house and stripped bark off a tree.

A piece of the metal letterbox ended up across the street in a neighbour's yard.

Another piece was found in the driveway of a neighbour a few houses down.

The remains of the letterbox included a red wick, used for detonation.

When Jack Tomlinson heard the blast, he thought a gas bottle had exploded. Another neighbour said the blast knocked ornaments off his window sill.

Witnesses saw two offenders outside Mr Heath's house shortly before the blast happened. They were seen running down the road and into Helen Street.

Another resident believed a group may have been involved in the incidents.

Damien Ryan was walking down Livingstone Street on Sunday morning, headed for a surf.

He found a sharp piece of metal on the path about 30 metres from the explosion.

Mr Ryan said the blast presented a "significant danger".

"It's not a little firecracker. It was strong enough to have seriously damaging effects."

Police said they were investigating the explosions.

"Windows of cars and two houses on Dent and Livingstone streets were damaged. No injuries have been reported," a police statement said.

Police Rescue safely removed the suspicious item from the Kilgour Avenue letterbox.

Police are appealing for information or dashcam footage. Phone 4929 0999 or Crime Stoppers 1800 333 000.