Emergency services were called to the Morriston area of Swansea on Monday morning following reports of a major explosion at a house.
As per the latest reports, one person is unaccounted for, and three others have been taken to hospital.
The first calls reporting the incident came in at around 11.20 am, and emergency services were quick to arrive on the scene.
Police have cordoned off the area, and Clydach Road remains closed, with traffic being diverted.
The explosion was so loud that it could be heard from miles away.
Two properties have been extensively damaged, and neighbouring properties have also been affected.
An investigation into the cause of the explosion, that was heard from miles away, is now underway.
A spokesperson for Wales & West Utilities said: “We were called to reports of an explosion at a property in the Clydach Road area of Swansea this morning (13 March) and immediately sent a team of engineers.
“On arrival, we found that there had been severe structural damage to the property and the emergency services were in control of the scene. We are now working with them to make the area safe – as we do on all incidents of this nature.
“We do not yet know the cause of the explosion and our engineers will continue to support the emergency services as they carry out their work.”