Singapore Day is a pre-registered event for Singaporeans and their families, and admission is by ticket, the organiser said on Tuesday, after an Australian man claimed that he and his father were turned away from the event in Sydney because they were Caucasian.

"Admission is by ticket for purposes of crowd control and catering. These are indicated on our website." said a spokesman for the Overseas Singaporean Unit (OSU) under the Prime Minister's Office.

"Singaporeans could bring along a guest who might be non-Singaporean, and also attend with family members who are non-Singaporeans as a family. Singapore Day 2013 was attended by Singaporeans, their family members and friends, of all races."

Singapore Day. which aims to keep Singaporeans living abroad connected to their home country, has been held in different cities like New York and Shanghai.

It was held in Sydney for the first time, at the Royal Botanic Gardens, on Saturday. The Straits Times understands that the Australian man and his father did not have tickets to the event.

The man, "James", rang Australian radio station 2GB on Monday to tell how he and his father were turned away because they "were not Singaporean". He added that people of Asian descent seemed to be allowed in, but he and his father were singled out because they were "clearly Caucasian". DJ Ben Fordham, who took James' call, said such discrimination was "disgraceful".

Australian newspaper The Daily Telegraph also reported that callers said "white people were turned away in droves".

Royal Botanic Gardens' deputy executive director Brett Summerell told The Telegraph that he would "see if it's appropriate for the Botanic Gardens to be involved with (OSU) in the future".

But when contacted, he told The Straits Times that he received only three phone complaints about people being excluded, and that it was protocol to review all events anyway. The event attracted more than 6,000 Singaporeans.