Saint Petersburg (AFP) - More than 100,000 people Wednesday signed an online petition against the handover of a flagship cathedral in the Russian city of Saint Petersburg to the Orthodox Church.

Local authorities in Russia's second city announced Tuesday night that Saint Isaac's Cathedral, which had been transformed into a museum in the Soviet era, would be returned to the powerful Orthodox Church.

The authors of the petition -- which was launched on change.org and addressed to President Vladimir Putin and Saint Petersburg Governor Georgy Poltavchenko -- fear the move could restrict tourists' access to a landmark of Russia's imperial capital and spell the end of the concerts that are staged there regularly.

"In my opinion this is a grave mistake," local opposition lawmaker Boris Vishnevsky wrote on his Facebook page, vowing to fight the decision.

Local media reported that 3.9 million tourists visited the cathedral last year, earning it more than 800 million rubles ($13.3 million).

The Church in 2015 had asked local authorities to hand over the cathedral, a request they rejected at the time.

Saint Isaac's, built by French architect Auguste Ricard de Montferrand between 1818 and 1858, was the Russian Empire's main cathedral.

It became a museum of atheism in the early Soviet era before being converted into an art and history museum in 1937.

Religious services during major religious holidays resumed at the cathedral in the 1990s.

The Orthodox Church's influence has grown dramatically under Putin's rule. The Kremlin strongman has approved the restitution of property the Church lost during the Soviet era.