The new Nokia smart phone Lumia 800 is shown off at Nokia world, London, Oct 26, 2011. [Photo/Agencies]

LONDON - Nokia unveiled two sleek new Microsoft Windows phones on Wednesday in time for Christmas, a first step in the ailing cellphone maker's fightback against Apple and Google.

Chief Executive Stephen Elop presented the two new smartphones, the first fruits of his big bet on Microsoft software, to a 3,000-strong audience in London, saying they represented the beginning of a new era for the Finnish giant.

"It's a new dawn for Nokia," Elop said as he unveiled the high-end Lumia 800 and mid-range Lumia 710, which will go on sale in key European markets next month.

In an interview with Reuters, Elop said the world's biggest cellphone maker had transformed itself during his 13-month tenure, which has seen a shake-up of senior management and thousands of lay-offs.

"It is a different company operating on a different clock speed," he said. "The amount of effort and passion and work that's been accomplished that we were able to show off today is the best evidence of that."

Nokia shares, which have halved in value since Elop announced his high-risk partnership with Microsoft and ditched its old software platform in February, were up 3.1 percent at 1323 GMT, outperforming the wider market.

Elop said the new phones' minimalist design and superior navigation features would make them stand out among rival Windows phones, some of which have been faster to market with Microsoft's new Mango mobile platform.

Christian Lindholm, a partner at design agency Fjord who formerly managed Nokia's classic S60 and S40 user interfaces, said the new phones showed a renewed confidence in Nokia's traditional strengths.

"They're getting back to their roots -- simplicity," he said. "They've stripped out the noise and focused on what people need to communicate, navigate and socialise."

The new Nokia smart phone Lumia 710 is seen on display at Nokia world, London, Oct 26, 2011. [Photo/Agencies]