Local actor Tosh Zhang has apologised after being called out for discrimination.

On Wednesday, the 29-year-old was named an ambassador for this year's annual Pink Dot event, which aims to raise awareness of issues that impact the daily lives of lesbian, gay, bisexual, transgender and queer (LGBTQ) people.

The theme of this year's event is Against Discrimination.

On Thursday, Facebook user Sarah Yip expressed her surprise at Zhang's appointment, and posted screenshots of some of his tweets from 2010 to 2013.

The tweets by Zhang - known for his role in the Ah Boys To Men movie series, and who also goes by the name Tosh Rock - made several discriminatory comments about LGBTQ people, including their physical appearance.

Pink Dot issued a statement on Thursday, calling his comments "homophobic and misogynistic".

It said: "Tosh Zhang's tweets from 2010 to 2013 that surfaced today, just a day after we named him one of our Pink Dot 11 Ambassadors, are deeply distressing. The hurt and harm that such language can cause is all too familiar to us."

The statement added that Pink Dot is reaching out to Zhang to clarify his stand and discuss further actions.

In the post on Facebook, Ms Yip said she was not asking for him to be removed from his role, but added that it is important for someone in his position to be held accountable.

Zhang replied on her post, apologising for the tweets.

He said: "I'd like to personally apologise to you and all members of the LGBTQ community which I have hurt with my extremely insensitive tweets from years ago. I take full responsibility for my hurtful words and I'd like to apologise to you and everyone who is affected."

The Pink Dot event, which is now in its 11th year, is expected to take place at Hong Lim Park on June 29.