A vandal damaged the giant portrait of China's late Chairman Mao Zedong that hangs over the Forbidden City on Saturday, prompting police to clear the area and adjacent Tiananmen Square, witnesses said.

Most of the picture was intact, but workers could be seen in a crane cleaning the lower left area of the huge portrait, which appeared damaged by soot after the vandal hurled a burning object at it. Police were swarming the area.

Traffic could pass by, but Tiananmen, the symbolic heart of Communist China, was temporarily cleared of the visitors that normally crowd the square on weekends and the tourist-clogged entrance to the Forbidden City was emptied.

Police later let visitors back onto the square, which remained under tight security.