Several letterboxes on Queensland's Sunshine Coast have been filled with crude, cheaply made explosives and detonated, causing major damage and prompting a warning from police that residents are at risk of injury.

Key points: Police say one incident exploded a brick letterbox and sent fragments flying metres in the air

Police say one incident exploded a brick letterbox and sent fragments flying metres in the air Several of the explosions occurred late at night, with the results only obvious the next morning

Several of the explosions occurred late at night, with the results only obvious the next morning Marilyn Robinson says she found debris spread for several metres across her front yard and driveway

Police said dozens of letterboxes had been destroyed across the region.

Officers said they believed young people were responsible for the destruction, with the explosions commencing at the start of school holidays.

In one incident at Little Mountain, a device made from a soft drink can exploded and destroyed a brick letterbox, sending steel parts of the letterboxing flying metres through the air.

At Parrearra, south of Mooloolaba, Marilyn Robinson said she heard an explosion as she was going to bed.

"My neighbours next door, we all came running out thinking it was at the back of our houses, and we couldn't see anything," she said.

"Then the next morning I had to go out at 8 o'clock, reversed past my letterbox and, lo and behold, that's where the explosion was. And it was very big.

"Parts of it went across the road and everything. If a car had been there, it could have damaged it, and people wouldn't be walking past at that time of night, but they could have been hurt."

Explosive devices have been detonated inside multiple letterboxes on the Sunshine Coast. ( Supplied: Queensland Police Service )

Ms Robinson said the debris from the letterbox spread several metres.

"All across, over to a tree, all over the road and all down my driveway, there was bits in the bushes. It was quite large, quite large," she said.

Kerry Anthony said he and his wife were woken by the explosion on the weekend but could not figure out where it had come from.

He said the street was quiet most of the time.

"Initially I thought it was thunder — I thought 'what the hell was that?' It was far enough away that I wasn't concerned," Mr Anthony said.

"You don't really want to open your letterbox and it go kaboom."

Police have warned residents to be vigilant after several letterbox bombs were detonated on the Sunshine Coast. ( Supplied: Queensland Police Service )

In another incident at Mountain Creek, the blast occurred near the front door.

Inspector Mark Cordwell said the letterbox bombings pose a risk not just to residents and neighbours but also those making the explosives.

"They also cause major damage to property and have a high risk of starting fires," he said.

"I would hate for an elderly person or resident to sustain serious injuries after innocently investigating a disturbance outside their home and being caught in one of these explosion."