Florida condo president warned of 'accelerating' damage to building
People visit the makeshift memorial for the victims of the building collapse, near the site of the accident in Surfside, Florida, north of Miami Beach on June 27, 2021(AFP)

The chairman of the condo association at the seaside apartment building that partially collapsed last week in Florida described "accelerating" damage to the building in a letter to residents in April.

The building was assessed inn 2018 by engineers who found problems including major structural damage below the pool deck, says the letter from Jean Wodnicki.

But Wodnicki says in the letter, obtained by CNN and other news outlets, that the concrete deterioration has since been accelerating.

"The roof situation got much worse, so extensive roof repairs had to be incorporated," it says.

The confirmed death toll in the collapse of the Champlain Towers South building on Thursday now stands at 11. Another 150 people are unaccounted for.

Questions are mounting as to how the residential building in the Miami area could have collapsed so quickly and violently.

The 2018 engineering report by Morabito Consultants did not say if the building was at risk of collapse.

That company did provide a $9.1 million estimate to the condo association for what it would charge to make "extensive and necessary repairs."

That figure rose as it became apparent more repairs were required under the county's 40-year recertification process and in April the Champlain Towers South condo association approved a $15 million assessment, according to CNN.

Payments were set to begin a week after the collapse, the network reported.

Friends and neighbors of the building's occupants held a vigil on a nearby beach on Monday evening, clutching white roses and sobbing as the group burned incense and played a gong.

Glow sticks and dirt laid on the sand spelled out the word "HOPE," while down the coast at the ruins of the building, the sound of rescuers' power tools carried on through the night with no indications that anyone had recently been found alive.