By Greg Torode and Grace Li

HONG KONG (Reuters) - Tens of thousands braved typhoon rains on Monday to demand China live up to its promise to allow fully democratic elections in Hong Kong in 2017 amid mounting fears of increased meddling by Beijing's Communist Party leaders.

The former British colony returned to Chinese rule on July 1, 1997, with the promise of universal suffrage as an "ultimate aim" in its mini-constitution, making it potentially the first place on Chinese soil to enjoy fully democratic elections.

Protesters marched and chanted, undeterred by the lashing rain as the march began, some carrying British colonial Hong Kong flags and pro-democracy banners along with umbrellas.

Younger activists have become increasingly politicized. Surveys show they identify themselves more as Hong Kong citizens than Chinese nationals - a trend that alarms Beijing, which is eager for the city to show more "patriotism" to the motherland.

Despite China's pledge to allow a direct poll for the city's leader in 2017, recent signs from senior Chinese officials have raised concern Beijing may somehow try to rig the rules to screen out opposition candidates from taking part.

"I just want to do my part to tell Beijing not to crush Hong Kong," said retired accountant Dominic Wong, 70. "This is my first protest. Hong Kong leaders have to do more to stand up to Beijing."

Qiao Xiaoyang, the head of the law committee of China's parliament, said in March that any candidates for the 2017 election must love Hong Kong and that opposition pro-democracy candidates who confronted Beijing wouldn't be acceptable.

Even before thousands massed in a downtown park for Monday's rally, there were unusual signs of tension elsewhere.

Executives of the popular Apple Daily newspaper, known for its anti-China, pro-democracy stance, said tens of thousands of copies of two editions of the newspaper had been torched in recent days by masked men targeting distribution points.

The home of the paper's owner, Jimmy Lai, was rammed by a car with a machete, an axe and a threatening message left in the driveway. Lai's group has offered a HK$1 million ($128,000) reward for tracking down those responsible.

Activist lawmaker Leung Kwok-hung said he was threatened by an anonymous phone caller on Saturday who told him to steer clear of the march or "face the consequences", but he still hit the streets.

"Universal suffrage now," he shouted during the protest.

The march is held every year, but this year's event is being seen as a forerunner to a wider campaign of choreographed civil disobedience over the next year.

The Occupy Central movement is demanding firm government proposals towards 2017 and is planning to shut down Hong Kong's financial district with a mass rally on July 1 next year - threats sparking alarm in Beijing.

"I'm not sure what the numbers are but it is looking very positive for Occupy," said Benny Tai, one of the organizers of Occupy Central. "We can see for sure that people are committed."

The march, which also saw thousands rally in support of a medley other social causes including poverty alleviation and press freedom, took place with leader Leung Chun-ying battling slumping popularity ratings and a series of scandals involving his cabinet.

A Chinese University poll last Friday showed that nearly half Hong Kong residents had no confidence his performance would improve in the coming year.

Leung said Hong Kong would begin consultations on deciding the exact scope of the 2017 elections "at an appropriate time".

"Working to implement universal suffrage in the 2017 chief executive election is key to the current government," he said.

The director of Beijing's Liaison office in Hong Kong, Zhang Xiaoming, said Hong Kong needed to be "harmonious and rational" but said the protests were a sign that Hong Kong still enjoyed "full freedoms and rights".

(Additional reporting by James Pomfret and Venus Wu; Writing by James Pomfret; Editing by Nick Macfie)