Ekachai was arrested while he was on his way to Bangkok's Dusit police station to hand himself in, and Bunkueanun was taken into custody after he surrendered to police, the lawyers group said.

The decree, which came into effect in the Thai capital, bans gatherings of more than five people and includes a nationwide ban on publishing and broadcasting news and information -- including online -- that incites fear among the public.

In a mass show of defiance, thousands of protesters hit the streets of Bangkok for a third consecutive night on Friday, chanting, jeering at police, and waving lights from their cell phones.

Police used water cannon to clear the demonstrators, who had gathered in Bangkok's main business district. Thai Public Broadcasting Service showed rows of security troops advancing on the site, with a water cannon vehicle behind them, before spraying water on protesters who held out umbrellas to shield themselves.

Crowds could be seen dispersing from the site, as police warned through a loudspeaker that demonstrators would be detained if they stayed.

In a speech made on Thursday, and broadcast on national TV Friday, Thailand's King Maha Vajiralongkorn said the country needed the people who "love the monarchy."

He made no direct reference to the ongoing protests, which are expected to continue through the weekend.

Student-led demonstrations and marches that have been ongoing across Thailand since July have escalated in recent weeks. Protesters are calling for a new constitution, the dissolution of parliament and resignation of Prime Minister Prayut Chan-o-cha, as well as an end to intimidation of government critics.

An increasingly central demand is the reform of the country's monarchy in order to curb King Maha Vajiralongkorn's powers and ensure a true constitutional monarch under a democratic system.

Prime Minister Prayut responded to calls for his removal Friday saying, "I won't quit."

In a news conference following a special cabinet meeting, Prayut said the cabinet had approved the emergency decree and that it could stay in place for up to 30 days.

"It (the decree) will be used for only one month or even shorter if the situation returns to normalcy," the Prime Minister said. "It doesn't aim at harming anyone. Recently who have been hurt? Mostly are the officials. This means the situation is irregular."

Prayut also warned young protesters not to violate the law and asked the parents to monitor their kids.

"For those students, should the parents do their best in taking care of their children as I don't want to see any consequence, it's quite harmful. I don't know what the mastermind really want," he said.

Protesters have turned out in Bangkok every day this week since Tuesday and coincide with King Vajiralongkorn's return to Thailand for a host of royal duties, including marking the memorial day of his father, the late King Bhumibol Adulyadej.

On Wednesday, thousands of protesters marched en mass from the city's Democracy Monument and broke through a police barricade to camp outside Prayut's offices late into the night.

Authorities stepped up security this week, deploying about 15,000 police to control crowds on Wednesday.

The Thai Lawyers For Human Rights said that 51 people have been arrested and are facing legal action following the anti-government protests in Bangkok this week.

Among them were several prominent activists including student leader Panusaya "Rung" Sithijirawattanakul, human rights lawyer and protest leader Arnon Nampa, and protest leader Parit "Penguin" Chiwarak.

Details surrounding the grounds for the 51 arrests have not yet been released.