Several dozen people have been detained at a rally to protest the construction of a cathedral in a popular park in Russia's fourth-largest city.

Russian news agencies on Thursday quoted local court officials as saying that 33 people were detained in the early hours and are expected to face the court for an illegal gathering. OVD-Info, a group that monitors arrest of civil activists, says it logged 70 detentions.

Protests in Yekaterinburg entered their third consecutive day on Wednesday as riot police were dispatched to the park in the city center where two local tycoons are planning to build a new cathedral.

Opponents say that the building would take away rare green and recreational space in this city of 1.5 million people.