Some monks' representatives had called for the entire country to join them in their campaign to overthrow the government, which began eight days ago.
Monday saw marches in at least 25 towns and cities, including Mandalay, Sittwe and Pakokku.
Turnout estimates in Rangoon, Burma's biggest city, range from 50,000 to 100,000.
In doing so, they're putting their lives on the line.
Burma's ruling military junta has warned it is ready to "take action" against Buddhist monks leading mounting protests, state media have reported. Brig Gen Thura Myint Maung, minister for religion, warned them not to break Buddhist "rules and regulations" as Rangoon saw the largest march yet.
He blamed the protests on "destructive elements" opposed to peace in Burma.
The military government has so far showed restraint against the protests.
Monks are highly revered in Burma and correspondents say any move by the junta to crush their demonstrations would spark an outcry.
But there are fears of a repeat of 1988, correspondents say, when the last democracy uprising was crushed by the military and some 3,000 people were killed.
The regime in Burma has shown itself to be highly resilient and resistant to outside influence. One hopes that this uprising will finally shame the junta into reform.