BUCHAREST, Aug 27 (Reuters) - World-renowned orchestras return to Romanian capital Bucharest from Saturday for its George Enescu Festival, one of Europe"s biggest classical music events, with organizers urging concert-goers to respect rules as COVID cases rise. The 25th biennial festival will feature 3,500 artists from 32 orchestras, including the London Symphony Orchestra, the Academy of St. Martin in the Fields and the Royal Concertgebouw, and renowned conductors like Sir Simon Rattle, Vladimir Jurowski and Vasily Petrenko. A host of international artists, including pianist Yuja Wang, mezzo-soprano Joyce DiDonato and violinists Joshua Bell and Maxim Vengerov will be performing in concert halls which require audiences to wear masks and in some cases present COVID digital certificates. "We will need to learn how to live with all these regulations. I don"t think we will be here next time without masks," said conductor Paavo Jarvi, who will open the month-long festival. "I think this thing is here to stay and we need to learn to love and live with this new reality." Romania is trailing European Union vaccination lists, with just over a fifth of the population, or 5.2 million people, inoculated as distrust in state institutions grows. The EU state reported over 900 new coronavirus cases for the second consecutive day on Friday, its highest daily tally since spring, and officials expect the numbers to rise. "Vaccination and testing are the festival"s biggest challenges," said Mihai Constantinescu, executive director of the Enescu festival. "If we have them, we have a festival." "We appeal to everybody who wants to listen to good music. ... We must take all measures to keep the festival going until Sept. 26." The festival, named after Romania"s most famous composer, will also feature a record number of world premieres by contemporary composers, a direction dear to the festival"s artistic director, conductor Vladimir Jurowski. "The presence of 20th and 21st century music in this festival is spectacular, the amount of pieces performed is bigger than ever and we have such outstanding artists engaging with contemporary music," Jurowski said. "This is the future."