VATICAN CITY - Dust and sediments brought into the Sistine Chapel by 20,000 daily visitors and inadequate climate control are threatening to take a toll on the Renaissance treasure, the head of the Vatican's museums has warned.

Restoration workers removed "unimaginable quantities" of dust and residue from the famed chapel during a summer cleanup conducted at night after a four year gap, Antonio Paolucci wrote in the Friday edition of Vatican newspaper Osservatore Romano.

The chapel, which draws about 4 million visitors annually who flock to see its ceiling frescoes by Michelangelo, suffers from the pressures inflicted by pollutants, too many visitors and insufficient climate control, he wrote.

"If we want to preserve the Sistine Chapel in acceptable condition for future generations, this is the challenge that we have to win," he wrote in the newspaper.

Michelangelo's frescoes in the chapel show scenes from the Bible, most famously "The Creation of Adam", in which God reaches out to touch the outstretched hand of the first man, and the "Last Judgement". It is also where cardinals meet to elect the next pope.