A strong explosion has hit a well-known hotel in downtown Havana, tearing a gash several floors high into the side of the building and killing at least nine people, witnesses and Cuban state media say.

President Miguel Diaz-Canel, speaking from the scene of the disaster on Cuban television, said the explosion at the Hotel Saratoga had not been caused by a bomb, adding that a gas leak appeared to be the most likely cause.

State TV said the blast had left nine people dead and several injured.

After returning to the site of the deadly blast following a brief visit to two hospitals treating the victims, Mr Díaz-Canel called the incident a “regrettable accident.”

Hospitals continued to treat the wounded, and rescues were still underway, he said.

Photos from Granma, the Communist Party’s official daily, showed images of the multistorey hotel with walls apparently blown out.

“Everything indicates that the explosion was caused by an accident,” the Cuban Presidential Office said in a tweet, adding that at least 30 people have been hospitalised after Friday’s blast.

A Reuters witness saw smoke and flames coming from the building.

Police and rescue workers flocked to the area, cordoning off key points and buildings nearby including the historic Capitolio building.

A photo from the scene showed what appeared to be at least one body on the scene with a white cloth over it.

Nearby, ambulances were seen approaching a hospital in the old quarter of Havana surrounded by a crowd of doctors, nurses, police and curious onlookers.

The neoclassical style hotel was re-modeled by a British company after the fall of the Soviet Union and was considered the place to go for visiting government officials and celebrities for many years.

Recently, it had lost some of its shine with the opening of new hotels in Havana but was still a five-star venue.

The hotel had been set for a post-pandemic re-opening in four days, according to its Facebook page.

-with AAP