Tens of thousands of supporters of Thaksin Shinawatra, the deposed Thai prime minister, are heading to Bangkok, Thailand's capital, preparing for mass rallies aimed at toppling the government.
The United Front for Democracy Against Dictatorship - popularly known as the Red Shirts - staged early protests on Friday and said a "million-man march" was to be held during the weekend.
"Today we had some small groups gathering, this is not yet a rally. We want to build sentiment before Sunday," Jatuporn Prompan, a Red Shirt leader, said.
Friday's protests passed peacefully, and organisers have insisted the coming rallies will also be non-violent.
But concerns about possible unrest remain and the government is deploying a 50,000-strong security force. It has enacted a tough security law that allows authorities to impose curfews and limit movements.
Al Jazeera's Wayne Hay, reporting from the outskirts of Bangkok, said checkpoints had been set up on the main roads leading into the city.
"The military and police have set up these checkpoints to check for any weapons that may be taken into Bangkok by Red Shirt supporters," he said.
"The Red Shirts themselves fear that these checkpoints are in place to prevent them from going to Sunday's protest.
"So far there is no sign of that but military and police are certainly ready for any trouble that may arrive."
Thaksin is still very popular in many parts of Thailand, but no one is really expecting a million people to gather in Bangkok to protest, our correspondent said.
Supporters of Thaksin, who was ousted in a 2006 military coup, called the protests two weeks after Thailand's highest court confiscated $1.4bn of his assets, frozen after the coup.
The Red Shirts argue that the government of Abhisit Vejjajiva, the Thai prime minister, came to power illegitimately with the backing of coup leaders and the ruling elite, and they are demanding new elections.
Authorities are anticipating unrest triggered by the planned rally, citing the Red Shirts' last major protest in April last year, which descended into bloody clashes on the streets of Bangkok.
Armed guards stood at many banks and state buildings on Friday after government warnings of potential sabotage, including bombings.
Several schools were closed, and some companies allowed staff to work from home.
The weekend's scheduled start of Thailand's national soccer league season has also been delayed, while dozens of countries issuing some form of travel warning to their citizens.
For their part, the Red Shirts have accused the government of trying to create fear, and said they have no intention of occupying public or private buildings, including the two airports serving Bangkok.
One of them, Suvarnabhumi international airport, which was shut down by anti-Thaksin Yellow Shirt protesters in late 2008, is believed to have put contingency plans in place to deal with any attempts at disruption.
Source: Al Jazeera and agencies