BEIJING, July 1 (Reuters) - China's ruling Communist Party must keep pace with changing circumstances while safeguarding the advances it has made, President Xi Jinping said on Wednesday during celebrations for its 105th founding anniversary.

Xi did not identify specific opportunities or risks in his 40-minute speech at Beijing's Great Hall of the People, but analysts say slower economic growth and demographic decline pose key challenges for the world's second largest economy.

"China's development is currently in a period where strategic opportunities, and risks and challenges, coexist," said Xi, its most powerful leader since Mao Zedong.

He called for the party to coordinate better to tackle domestic and international issues.

Faced with external challenges from Western-led curbs on advanced technology to turbulent trade ties with the United States and tension over Taiwan, party leaders consider it a critical task to strengthen their grasp on all aspects of Chinese society.

Founded by just dozens of Chinese revolutionaries in 1921, the party now claims more than 100 million members, or 7.2% of China's population.

Today, its ambition is to transform itself into the world's "most powerful political party", from the world's "largest political party," the official Xinhua news agency said in an editorial this week.

Xi urged members to stamp out aspects harmful to the party's advancement and "purity", as well as "all viruses that erode the party's healthy body".

Since coming to power in 2012, Xi has worked to reassert the party's unquestioned authority at home, demand loyalty and unflinching discipline among its ranks, and expand China's global influence.

He has launched one of China's most sweeping graft crackdowns since Mao's day, investigating millions of officials at all levels, purging hundreds, along with top generals, in the years-long campaign.