Google announced Monday it will offer its personal assistant app Google Now to users of Apple devices, stepping up its challenge to its rival's Siri program.

"Google Now is about giving you just the right information at just the right time," Google's Andrea Huey said in a blog announcement.

"It can show you the day's weather as you get dressed in the morning, or alert you that there's heavy traffic between you and your butterfly-inducing date -- so you'd better leave now!

"It can also share news updates on a story you've been following, remind you to leave for the airport so you can make your flight and much more."

Google Now, which like Siri is a voice-activated software program -- will be available to users of Apple iPhones and iPads, which use the iOS operating system.

"Today, with the launch of Google Now on iPhone and iPad, your smartphone will become even smarter," Huey said.

The move comes with the two California tech giants in a fierce battle for domination of mobile operating platforms. Google's Android has taken the lead in smartphones and is gaining rapidly in the tablet market.

Google meanwhile has argued that Apple's Siri is a potential threat to its core search engine by allowing smartphone users to bypass Google for many searches, which can generate ad revenue.