Lancashire Police said a safety cordon had been put in place and nearby residents had been evacuated in the town some 25 miles north-east of Blackpool.
"We are asking people to please avoid the entire area while we deal with this ongoing incident," the force said.
The North West Ambulance Service tweeted that it had also sent units to the scene, with a priority to "ensure people receive the medical help they need as quickly as possible".
Electricity North West tweeted that it had paused electricity supplies to the area for safety reasons while the blast was being investigated.
A major incident has been declared after a reported gas explosion destroyed up to three terraced houses in Heysham, Lancashire.
Lancashire Fire said on Twitter that 10 units were called to a row of houses on Mallowdale Avenue around 2.30am on Sunday. Firefighters were searching a collapsed property.
Nearby residents said they heard a blast that sounded and felt like a "minor earthquake" or a bomb.
"A major incident has been declared after we (were) called to terraced houses on Mallowdale Avenue. It has been reported that there has been an explosion at a property and firefighters are searching the collapsed property," Lancashire Fire said.
No information on any casualties was immediately available, but several residents of the area tweeted that up to three houses had collapsed, and that emergency services sirens were heard near the scene.