More than 2,000 people attended Singapore's biggest protest in decades on Saturday to demand curbs on immigration amid growing public anger over an expected surge in the foreign population.

The peaceful three-hour rally at an officially designated protest zone was staged by a civic group after the government said foreigners could account for nearly half of the densely packed island's population in less than 20 years.

Organizers put the crowd, shielded by a sea of umbrellas from heavy downpours, at 4,000. Police said they were not monitoring the size of the crowd and AFP reporters estimated the turnout at more than 2,000, many of them clad in black.

"I think it's the largest protest in decades. It is also the first one where anger is directed squarely at the government," said Reuben Wong, an assistant professor of political science at the National University of Singapore.

"People are now more willing to air their grievances. They have been doing it on the Internet for the past few years, but it is new for them to physically come down in such numbers," he told AFP.

A government policy paper last month said the population could range between 6.5 and 6.9 million by 2030, with foreigners making up 45 percent because Singaporeans are not producing enough babies to sustain economic growth and support a rapidly ageing population.

Citizens currently make up 62 percent of the current population of 5.3 million.

Foreigners have been blamed for stealing Singaporeans' jobs as well as straining housing, transport and medical services.

A Chinese restaurateur in Singapore told the Global Times on Sunday that the discrimination against foreigners is common in the country.

"The elder generation treats Chinese immigrants with respect but the younger generation feels otherwise," said the restaurateur, who demanded anonymity, "Chinese immigrants receive less payment under the same work load compared to immigrants from Malaysia. Many felt disappointed and went back to China."

Liu Guofu, an immigration law professor from Beijing Institute of Technology, told the Global Times that it is common for citizens to blame immigrants for social problems. "Immigrants do have impact on local society, but they also contribute to the economy and help offset a falling birth rate."

AFP - Global Times