Tue Jun 23, 2015 12:03pm EDT San Francisco

Google Inc launched a free version of its music streaming service on Tuesday, as it sought to upstage the debut of Apple Inc's rival service next week.

Google Play Music has offered a $9.99 per month subscription service for two years but Tuesday's launch is the first free version of the streaming service. It is available online and will be available on Android and iOS by the end of the week, Elias Roman, Google product manager, said.

Apple said earlier this month it would launch a music streaming service on June 30 for $9.99 per month along with a $14.99 per month family plan, with a free three-month trial.

As with other streaming services, such as Spotify and Rhapsody, Google Play Music curates playlists. Users can tailor playlists based on genre, artist or even activity, such as hosting a pool party or "having fun at work."

"We believe this is a play that will expose a lot of people to the service," Roman said in an interview.

Unlike Google's subscription music service, the free service will carry ads, be unavailable offline and exclude certain songs.

Roman said millions of people look at Google Play Music each month but are not ready to pay for a subscription. By offering a free version of the service, he said, the search engine hopes more people will be compelled to pay for an upgraded version.

Ted Cohen, managing partner of TAG Strategic, a digital entertainment consultancy, said the timing of Google's launch was strategic.

"It's a smart time to do it with all the attention around Apple," Cohen said. "If they did it absent the Apple service, it wouldn't be the same story."

Google declined to say how many subscribers it has but said they more than doubled in 2014 from the previous year. But rivals Pandora, Spotify and Beats Music had far more mobile downloads than Google Play Music in 2014, according to data from analytics firm App Annie.