An anti-immigration rally in Singapore drew just 500 people on Saturday, eight months after a similar protest by the same group generated one of the city state's largest protests since independence.

The peaceful three-hour rally, held at a park, was the third in a series of protests organised by a civic group after the government in January announced foreigners could account for nearly half of the densely packed island's population by 2030.

Authorities have since clarified that the forecast is not a population target, and have phased in measures to tighten foreign worker inflows.

"The momentum from the protests earlier this year has gone off, and the anger and emotion among Singaporeans is maybe no longer there," chief organiser Gilbert Goh told AFP.

Goh estimated the crowd at 1,000 but an AFP reporter on the scene said around 500 people attended the event at Speakers' Corner, a grassy park close to the central business district where protesters are allowed to address the public.

Speakers, including bloggers and activists, openly attacked the long-ruling People's Action Party (PAP) for favouring foreigners over citizens, and called on protesters to vote against it in the next general election expected in 2016.

Over 3,000 had attended a February 16 rally, just weeks after the release of a government policy paper that said the population could range between 6.5 to 6.9 million by 2030, with foreigners making up 45 percent because Singaporeans are not having enough children to sustain economic growth.

A subsequent rally in May also attracted more than 3,000 people, making them the country's biggest protests in decades.

Goh said he was unlikely to organise another anti-immigration protest due to the waning support.

"But we are happy that our protests have pushed the government to make a few policy changes," he said.

Authorities have been phasing in various measures to tighten foreign worker inflows, including a new policy announced in September requiring companies to show proof they first tried to recruit local citizens before hiring foreign professional workers.

Singapore citizens -- who currently make up 61 percent of the city state's 5.4 million population -- accuse foreigners and permanent residents of competing with them for jobs, housing, schools and space on public transport.

They have also complained that the rapid foreigner influx in previous years is eroding their national identity.

The discontent spilled into general elections in 2011 when the PAP garnered its lowest-ever vote count after more than 50 years in power.