Police in Azerbaijan have detained about 35 people after a group of opposition protesters held a small rally in central Baku on the eve of the Eurovision song contest final.

The gathering on a busy promenade beside the Caspian Sea in the capital was called on Friday by the Public Chamber opposition alliance, which brings together the main opposition parties in the energy-rich nation.

But police grabbed the protesters from the crowd of several dozen people as they shouted "Freedom!", putting them in vans.

One young woman screamed as she was shoved into the vehicle.

Ehsan Zahid, Azerbaijan interior ministry spokesman, described the rally as a disruption of public order.

"An attempt was thwarted by a group of youths to disrupt the public order," Zahid said. "Some of them were issued warnings."

Zahid said the demonstrators were moved to another location and later released.

'Totalitarian regime'

The busy public place filled with journalists and observers, including some representatives of Europe's security body OSCE, as police officers struggled to identify more protesters in the crowd.

"I must say I did not expect them to crack down like this," said Anders Nielsen, one of the observers from the Norwegian Helsinki Committee, who came for Eurovision.

"What we are truly seeing here is a totalitarian regime that cracks down on anything that looks like opposition," he told the AFP news agency.

Azerbaijan has made an effort to put on the international Eurovision song contest decorating its Caspian capital with contest insignia and constructing the Chrystal Hall venue.

But the festivities have been overshadowed this week by arrests of dozens of opposition supporters who have seized on the opportunity to draw attention to the country's rights record and issues like political prisoners.

Opposition groups are trying to use Saturday's event to publicise rights issues they say have been overlooked for years.