Thai Prime Minister Thaksin Shinawatra says he is prepared to declare a state of emergency if mass protests against his administration turn violent.
As he spoke to reporters in rural northeastern Thailand Tuesday, at least 60,000 people marched to his office in the capital Bangkok, vowing to keep it surrounded until he quits.
The march began early Tuesday after an all-night rally in a field next to Bangkok's Grand Palace, which was attended by around 40,000 people.
The rally was timed to take place during a cabinet meeting, and Mr. Thaksin was to chair the gathering by video-link from his location.
Sunday evening, all six broadcast TV channels aired footage of the Thai king's mediation of the bloody political turmoil of 1992 in a royal show of concern about the current political situation
The Thai capital has experienced regular protest rallies since late January, when Mr. Thaksin's family sold the telecommunications firm he founded for nearly $2 billion without paying taxes.
Such rallies have been peaceful in the past, but police are concerned about possible conflict, as Mr. Thaksin's supporters are in the capital for their own rally.
Some information for this report was provided by AFP and AP.