A fire raged through a 19th century cathedral in this former imperial capital Friday, collapsing the main rooftop dome and sending clerics scurrying to save treasured icons.

The fire erupted in the early evening and burned through scaffolding outside the soaring blue central dome of Trinity Cathedral, a duty officer at the Russian Emergency Situations Ministry said.

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The central dome collapsed and one of four smaller cupolas surrounding it — painted a striking light blue and in some cases spangled with gold stars — was also destroyed, St. Petersburg emergency department spokeswoman Lyudmila Rubasova said. There were no reports of injuries, she said.

Firefighters battled to save the other three cupolas as emergency workers and church employees removed icons and other religious articles. A helicopter brought in to fight the blaze dumped water on the historic structure.

About four hours after the blaze broke out, Rubasova said one of the three remaining cupolas had been damaged but that the fire was contained. A department spokesman later said the fire had been extinguished.

The cause of the fire was not immediately known, but acting St. Petersburg emergency department chief Leonid Belyayev said the blaze apparently started on scaffolding on the outside of the church, which was undergoing restoration.

He said the most valuable icons and other items had been saved, and that structural damage beneath the roof area was minor.

The cathedral was consecrated in 1835. State-run Rossiya television said the main dome was the second-largest wooden cupola in Europe, and Channel One said that writer Fyodor Dostoyevsky was married there.

It was used as a storehouse during the Soviet era and was returned to the Russian Orthodox Church in 1990.