BANGKOK (AP) — The authorities in Bangkok shut down mass transit systems and set up roadblocks Saturday as Thailand’s capital faced a fourth straight day of determined anti-government protests.

The protesters have been doing their best to elude the authorities, using social media to assemble followers before police have time to block them. The government has announced plans to take legal action against Twitter and Facebook accounts that announce the protests, but fresh calls to action were posted Saturday.

The protesters are calling for Prime Minister Prayuth Chan-ocha to leave office, the constitution to be amended to make it more democratic and the nation’s monarchy to undergo reform. The protests have been called in defiance of a state of emergency imposed on Thursday.

All stations of Bangkok's elevated Skytrain mass transit system were ordered closed Saturday afternoon in an effort to thwart protests. A line of the underground MRT system was also shut, and police blocked off several roads. Organizers had called for their followers to meet at Skytrain stations pending further instructions.

Groups of protesters met at many of the stations that were closed, in effect establishing a protest presence across the city. In a further twist, organizers issued a fresh advisory for followers to gather at three stations outside the city's central area, where access was easier, especially for people living in the suburbs.

Police on Friday had also tried to block demonstrators, but failed when protest organizers announced a last-minute switch of venue.

Friday’s rally was broken up by a large contingent of riot police backed by water cannons after at least 1,000 people had gathered. It was the first time the authorities have employed such forceful tactics against the student-led protests. Both Thursday’s and Friday’s protests were held in normally busy areas of central Bangkok.

“The government has been pushing us to the cliff and now we have nowhere to go. We need to stand right now; if not now, then we don’t know when,” said one protester, a 26-year-old who declined to give her name for fear of getting in trouble with the authorities..

Police took control of Friday's rally site after about an hour, though continued to engage with some stragglers. Flash protests were launched in solidarity at several universities around the country.

“From the dispersal of protesters on the evening of October 16, we have learned that the government and military have established themselves as the enemy of the people,” said a statement issued after Friday’s events by the People’s Party, the umbrella organization for the protesters. Most of its top leaders have been arrested.

The call by the protesters for reform of the monarchy has significantly raised the political temperature in Thailand, angering many older conservative Thais for whom any critical discussion of the monarchy is tantamount to treason.

King Maha Vajiralongkorn and other key members of the royal family are protected by a lese majeste law that has regularly been used to silence critics who risk up to 15 years in prison if deemed to have insulted the institution.

Prayuth’s declaration of a state of emergency said the measure was necessary because “certain groups of perpetrators intended to instigate an untoward incident and movement in the Bangkok area by way of various methods and via different channels, including causing obstruction to the royal motorcade.”

He was referring to an incident Wednesday that showed some members of a small crowd heckling a motorcade carrying Queen Suthida and Prince Dipangkorn as it slowly passed.

On Friday, two activists were arrested under a law covering violence against the queen for their alleged part in the incident. They could face up to life in prison if convicted. They denied any wrongdoing.