Travellers being urged to avoid rally sites, stock up on cash, food and water.
Many countries have advised their nationals to stay away from demonstration sites on Monday and ensure that they have enough cash on them, a fully-charged communication device as well as enough food and water to last a while. They have also been advised not to wear red or yellow.
"Participating or showing support in any form to any of the parties is strongly discouraged," the Philippines Embassy in Bangkok said on its website.
"For information, the red and yellow colours are closely identified with some of the parties involved," it said referring to the colours associated with political conflict over recent years.
People who support the Yingluck Shinawatra government have been wearing red, while anti-government groups, who used to wear yellow, have now chosen to wear the national flag along with a whistle.
Meanwhile, the United States Embassy has warned its citizens to be careful, because although mass rallies have been generally peaceful over the past few months, there have still been some deaths and injuries.
"Even demonstrations that are meant to be peaceful can turn confrontational, and escalate into violence without warning," the US Embassy warned.
The People's Democratic Reform Committee plans to set up rally sites at several major intersections in Bangkok and significant areas, namely Asok, Pathum Wan, Lumpini, Victory Monument, Ratchaprasong, Lat Phrao and the Government Complex at Chaeng Wattana.
Protests might erupt in other areas with little prior notice and subsequent events are unpredictable as protest leaders have declared that they plan to continue rallying after Monday, the embassy said.
"We advise you to plan ahead. It is prudent to ensure you have a week's supply of cash, keep your mobile communications devices charged and stock a two-week supply of essential items such as food, water and medicine," the US Embassy said.
The Foreign Ministry said yesterday that as many as 45 countries had issued warnings for their citizens to stay away from large crowds, rally sites and avoid travelling during the shutdown.
Kuwait and the United Arab Emirates have even advised their citizens to cancel travel plans for the time being, ministry spokesman Sek Wannamethee said, adding that this may affect the medical industry as people from the Middle East often come to Thailand for treatment.
This comes after Thailand recently began offering citizens from these two countries visa-free entry for 90 days, he said.
Citizens from Taiwan, Hong Kong, Russia and Oman, for whom Thailand is a favourite destination, have also been advised to stay away.