The Lithuanian Family Movement staged the rally to protest against the restrictions for those who do not have the national COVID-19 immunity certificate, the requirement to wear facemasks in schools and other measures to curb the spread of the pandemic, as well as against an initiative to legitimize gender-neutral partnerships, and the Istanbul Convention.
Some demonstrators waved Lithuanian flags and held placards that read "No to animal passports" or "George Soros out of Lithuania".
Raimondas Grinevicius, the Family Movement's leader, urged the government to cancel the restrictions, set to take effect next Monday, for people who do not have the immunity certificate.
"This is the step to start with to calm down the passions, because Gedimino Avenue may be too small to accommodate all the protesters during the next rally," he told the crowd.
"We have managed to block the partnership bill and had the Istanbul Convention shelved. We chose [to protest] today, September 10, to let the members of the Seimas know that we are not going to give up."
Arturas Orlauskas, another organizer, noted that the rally was taking place amid heavy police presence.
"Despite the hurdles being created [by the authorities], we have all gathered here today," he said.
A pre-recorded video greeting from Hungarian Prime Minister Viktor Orban's Fidesz party was played during the rally, and German politicians from the right-wing AfD party addressed the crowd from the stage.
Police said around 3,000 people had gathered on the square, but the number of participants was still growing. No incidents have been recorded so far.
The organizers sought but were denied a permit to hold Friday's rally outside the parliament after the August 10 protest there turned into a riot, leading to several dozen arrests and pre-trial investigations.