BANGKOK (BLOOMBERG) - Thai protest leaders plan to revive demonstrations as soon as the country's worst coronavirus outbreak starts to ease, adding to the government's challenges as it comes under fire for a slow vaccine roll-out.

After a months-long hiatus due to a spike in cases, protest leaders say they are working to draw fresh support from frustrated residents for a movement that began last year with calls for Prime Minister Prayut Chan-o-cha's resignation and unprecedented reforms of the monarchy.

The authorities have faced increasing public criticism for Thailand's third wave of Covid-19, which has more than quadrupled total cases since early last month.

"When we return to the streets, there'll be even more people joining us," Ms Patsaravalee Tanakitvibulpon, one of the protest leaders, said in a phone interview this month, adding rallies will start again as soon as the infection risk has been minimised.

"We can't wait too long. We want to take advantage of this period when there's a lot of anger."

Any return of large-scale protests in the capital Bangkok and cities across Thailand risks upending the government's plan to reopen the country for tourism, a sector key to putting the economy on the path to recovery.

Its contraction has continued into the start of the year, with gross domestic product in the first quarter shrinking 2.6 per cent from a year earlier. Mr Prayut's administration plans to borrow an additional US$22.3 billion (S$29.7 billion) to fund measures to counter the Covid-19 outbreak, Bloomberg reported this week.

Mr Prayut last week called for cooperation in efforts to contain the virus, saying the government's priority is to control infections and ramp up vaccinations. Government spokesman Anucha Burapachaisri did not immediately respond to questions on the protesters' plan to return to the streets.

"We're facing a terrible enemy that we've never encountered before called Covid-19, and the only way we can defeat this enemy is through unity, not conflicts or division," Mr Prayut said last week.

"The future of Thailand will depend on all of us. This is not the time for politics."

Opposition parties have called for the government to quit over its "mistakes", and more than a million Thais have joined a Facebook group called "Migrate" to discuss ways to leave the country for good.

The Bloomberg Covid-19 Vaccine Tracker shows Thailand's vaccination program currently covers about 1.8 per cent of the population, less than poorer neighbours Cambodia, Laos and Myanmar.

A survey of 2,082 respondents last month showed only 39.19 per cent believed the government could cope with the current outbreak, while the rest said they were either unsure or thought the government might not be able to handle the situation, according to the Suan Dusit Poll, one of the most prominent pollsters in Thailand.

The majority said they were "more stressed" with the Covid-19 situation, and expected it to last longer than three months, with a possibility of a fourth wave.

Protest Crackdown

"Issues ranging from the outbreak to the economy have expanded the movement, and these people will come out as soon as they're able to gather again," said Dr Punchada Sirivunnabood, a visiting fellow at Singapore's ISEAS-Yusof Ishak Institute who researches Thai politics.

"If there's enough pressure, the government may be forced to dissolve the Parliament and hold early elections."

From mid-2020, the youth-led protest movement broke a long-held taboo about publicly discussing the monarchy, which sits at the apex of power in Thailand. It reached its peak late last year when hundreds of thousands of demonstrators joined calls for more transparency and accountability from King Maha Vajiralongkorn, Mr Prayut's resignation and a constitution rewrite to make it more democratic - all of which are still being pushed for by the protesters.

Still, the virus outbreaks have hurt the ability of protesters to maintain momentum. The government has also started cracking down on protesters and arresting leaders for sedition as well as royal defamation, which is punishable by as many as 15 years in prison for each instance. The government has said that it is simply enforcing the law and has not targeted any groups in particular.

"The government may think that by detaining key protest leaders, it can stop the movement, but we already have many new-generation leaders coming up to take charge," said another protest organiser Arthitaya Pornprom.

At least six protest leaders are currently detained awaiting trials, including three activists facing lese majeste charges, according to May 19 data from the Thai Lawyers for Human Rights.

A court could decide as soon as next month whether to detain protest leader Ms Patsaravalee, along with a dozen other activists facing charges, for giving speeches in October asking the German authorities to scrutinise the King's legal status in the European country, where he had previously travelled frequently.

"The more people they detain, the worse it'll look for them," Ms Patsaravalee said. "With the government doing so poorly with the outbreak and vaccinations, our messages resonate more than ever."