British singer Sarah Brightman has delayed the start of her training to be a space tourist but plans to go ahead with her flight, Russia's space agency said Friday.

Brightman, the soprano famed for her roles in musicals by her ex-husband Andrew Lloyd Webber, arrived in Moscow and was due to start training this week for her flight, planned for October, for which she will reportedly pay around $52 million.

But the 54-year-old has delayed her training at the Star City complex outside Moscow and has now left Russia to visit her sick mother, Alexei Krasnov, the head of manned flights at the Russian space agency, told TASS state news agency.

"She has gone away for family reasons, but she promised to be in Moscow on Sunday," Krasnov said.

He denied suggestions that Brightman could give up her place to a 51-year-old Japanese businessman who markets space tourism, Satoshi Takamatsu, who is also starting training to become a space tourist.

"There are no indications that she will abandon the flight," Krasnov said.

An official at the Yuri Gagarin cosmonaut training centre told TASS that Brightman was due to meet the staff on Thursday but "she got a cold and now it's all postponed till next week".

Brightman, who had her first hit with 1970s disco anthem "I lost my heart to a starship trooper", announced in 2012 that she would become the eighth space tourist.

Her trip outside the earth's atmosphere is being arranged by US firm Space Ventures.

Previous space tourists visiting the ISS on a total of eight trips have included the Canadian founder of the Cirque du Soleil, Guy Laliberte, and Iranian-American entrepreneur Anousheh Ansari, so far the only woman.

Brightman is expected to blast off to the International Space Station in a Soyuz craft with Russian cosmonaut Sergei Volkov and Denmark's Andreas Mogensen from the European Space Agency and spend 10 days in space.

She will have to pass a medical 40 days ahead of the flight.

Brightman will be the first professional singer to visit the ISS, although not the first to sing, as Canadian astronaut Chris Hadfied performed his version of David Bowie's "Space Oddity" in zero gravity in 2013. A video posted on YouTube was viewed more than 23 million times.