Twenty-two people, including a child, have been killed after a powerful explosion apparently caused by a natural gas leak that blew away outer walls from a luxury hotel in the heart of Cuba's capital.

No tourists were staying at Havana's 96-room Hotel Saratoga because it was undergoing renovations and was to reopen on May 10.

"It has not been a bomb or an attack. It is a tragic accident," President Miguel Díaz-Canel, who visited the site, said in a tweet.

Police cordoned off the area as firefighters and rescue workers toiled inside the wreckage of the hotel, which is about 110 yards (100 meters) from Cuba's Capitol building. 

The Health Ministry said the number of injured could rise as the search continues for people who may be trapped in the rubble of the 19th century structure in the Old Havana neighbourhood of the city.