A suspected gas explosion has injured at least 21 people and blown out at least two floors of a hotel in Texas.

Footage shows a massive plume of smoke rising from the hotel in Fort Worth as helicopters hover over the scene and officials secure bystanders and victims.

The incident, at the Sandman Signature Fort Worth Hotel, was reported at 3:30pm yesterday (Mon).

The area, spanning two blocks, has been sealed off.

The smell of natural gas persists but the Fort Worth fire department has not confirmed the cause of the explosion.

According to the fire department there was ongoing construction in the building and natural gas is the likely cause.

Craig Trojacek, from the Fort Worth fire department, said: "There is a smell of gas here in downtown. "

"We're not sure if the smell of gas was caused from the explosion and the fire itself or if that's what caused the explosion but that's what we're looking at."