The annual Pink Dot gathering will be held from around 0900 GMT at a downtown park -- the only place where demonstrations are permitted.

The carnival-like rally draws a diverse array of straight and gay participants decked out in bright pink attire including hats and even facial hair dyed in the colour organisers picked to represent the freedom to love.

Organisers said they expect the turnout to top last year's record of 20,000, making it one of tightly-governed Singapore's biggest public rallies in recent times.

But they stressed that the rally was not a protest but a show of support for lesbian, gay, bisexual and transgender people.

The term "Pink Dot" is a play on Singapore's nickname -- "The Little Red Dot" on the world map.

The event, held every year since 2009, usually passes without much controversy, but this year Muslim and Christian conservatives have mounted countermovements to display their opposition to the city-state's vocal gay rights activists.

Lawrence Khong, a senior pastor with the 10,000-strong Faith Community Baptist Church, on Friday chastised the government for allowing the event to take place at Hong Lim Park, Singapore's only free-speech zone.

Khong is a longstanding opponent of a campaign to repeal Section 377A, a provision in the Singapore penal code that makes sex between men a crime.

The provision dates back to British colonial and carries a maximum penalty of two years, but it is not actively enforced by the Singapore government.

"This is no good for Singapore. Why then is our government giving Pink Dot public space to push their agenda and grow their movement?" he said in a statement late Friday.

"I would like to see our government leaders draw a clear line on where they now stand with regard to this moral issue," he added.

The pastor has professed support for a separate peaceful protest led by Ustaz Noor Deros, a Singaporean Muslim teacher seeking to encourage "a return to values as guided by Islam".

Noor's "WearWhite" campaign has called on Muslims to shun Pink Dot and instead wear white garments to mosques later Saturday to attend special prayers usually held on the eve of the Muslim holy month of Ramadan.

Officials have avoided taking sides and have instead urged Singaporeans to practise restraint in debating LGBT rights.

Even though it is not enforced, the government, led by the long-ruling People's Action Party, says Section 377A has to stay on the books because most Singaporeans are conservative and do not accept homosexuality.

A survey of 4,000 citizens by the government-linked Institute of Policy Studies earlier this year found that 78.2 percent of the local population felt same-sex relations were wrong.