YANGON, Sep 24 (Reuters) Tens of thousands of people joined Buddhist monks on marches in Myanmar's former capital today in the biggest demonstration against the ruling generals since they crushed student-led protests nearly 20 years ago.
''I'm very excited and frankly I'm worried too,'' a teacher said as she watched the massed opposition in Yangon to 45 years of army rule that has impoverished the nation of 53 million people.
Protests were also reported elsewhere and residents in the northwest coastal town of Sittwe said it seemed the entire population of more than 100,000 people was marching with the monks.
''I've never seen such a big crowd in my life. The whole town came out,'' one said.
In Mandalay, 10,000 monks and people took to the streets and a demonstration also took place in Bago, just north of Yangon.
The ruling military junta, which had been silent since the monks' protests began six days ago, threatened them with legal action.
Minister for Religious Affairs Brigadier General Thura Myint Maung was quoted on state-owned radio as saying ''actions will be taken against the monks' protest marches according to the law if they cannot be stopped by religious teachings.'' Speaking to senior members of the State Monks Council, he said the protests were incited by ''destructive elements who do not want to see peace, stability and progress in the country.'' Earlier, five columns of maroon-robed monks, one stretching more than a kilometre (nearly a mile), marched from Yangon's Shwedagon Pagoda, the devoutly Buddhist country's holiest shrine, to the city centre where thousands of people filled five blocks.
''People locked arms around the monks. They were clapping and cheering,'' a witness said.
Some monks carried placards calling for ''Better Living Conditions'' and the ''Release of Political Prisoners''. Another banner said: ''May The Peoples' Desire Be Fulfilled''.
After holding prayers at the Sule Pagoda in the main business district, a crowd estimated at up to 100,000 marched to another pagoda and dispersed peacefully.
For the first time, the marchers included members of parliament elected in 1990 from the opposition National League for Democracy (NLD) two days after a dramatic appearance of support for the monks by detained NLD leader Aung San Suu Kyi.
''IT'S ABOUT REFORM'' What began as anger at last month's shock fuel price rises has become a wider movement against the generals, with one monk group calling for peaceful mass protests until the junta fell.
''There's no prospect now of the monks just deciding to abandon this. They are getting braver every day and their demands are getting greater every day, and it's much more overtly political,'' a Yangon-based diplomat said.
''It's now about Aung San Suu Kyi, it's about reform.
''The monks have got numbers and, if not immunity, then certainly it's much more difficult for the government to crack down on them than ordinary civilians,'' the diplomat said.
The United States, the loudest Western critic of the regime, expressed sympathy for the protesters and denounced the military.
Myanmar's regional neighbours, long frustrated by the generals' refusal to speed up reforms, looked on with worry.
''We hope that the ongoing protests will be resolved in a peaceful manner,'' said the Foreign Ministry of Singapore, one of Myanmar's biggest foreign investors.
There were no signs of trouble during today's protests, but rumours of an imminent crackdown swirled in Yangon. One rumour suggested hospitals were being emptied of non-critical patients.
The generals were due to hold a quarterly summit soon in their new capital of Naypyidaw, carved out of the central jungle. Dealing with the protests is sure to top the agenda.
The protests began on August. 19 and soon prompted a round-up of the democracy activists who organised them and now face up to 20 years in jail. As the protests have grown, they have drawn public declarations of support from the famous.
The country's biggest stars of the stage, screen and music, including Tun Eindra Bo -- Myanmar's equivalent of Angelina Jolie -- have formed a ''Sangkha Support Committee'' and pledged to provide the monks with whatever assistance they need.
''The fact these celebrities are joining in is very significant,'' said one Myanmar exile who listened to them giving interviews on Burmese-language foreign radio stations.
''The committee said they will move on with the struggle until the end,'' the exile said.
REUTERS GT RK2246