The wife of Hong Kong Chief Executive Leung Chun Ying has defended her eldest daughter over the latter's latest scandal, which involved the older woman being slapped twice by the younger one on camera during a night out to celebrate Halloween.

According to reports from the South China Morning Post and Apple Daily, a number of videos posted online show Ms Leung Chai Yan, 24, who was decked out in ghoulish attire and make-up, striking her mother Regina Tong twice in the face last Saturday night as she was being bundled into a taxi in the busy Lan Kwai Fong district.

It was not clear what caused the public outburst, but it is understood that the visibly drunk Ms Leung was causing a commotion on the streets before her mother appeared.

Ms Tong was seen recoiling in shock and cradling her face before attempting to get into the taxi with Ms Leung, who slapped her again and kicked her, then left in the taxi without her.

Ms Leung said to the crowd, which included reporters who had gathered at the scene around 3am on Sunday: "You know this mum is not my actual biological mum?"

But her friend quickly warned her not to say anything more.

When asked by reporters, Ms Tong denied the slapping and quickly left the scene on her own.

But she urged the media on Monday to leave her daughter alone, saying that she was drunk and wanted to protect her friends from the crowd of reporters, and had not meant to offend anyone, reported the South China Morning Post (SCMP).

"Chai-yan is a kind-hearted girl... (She) is innocent," Ms Tong was quoted by the SCMP as saying, adding: "She needs rest."

Netizens have flocked to Ms Leung's Instagram account to criticise her for being unfilial.

Ms Leung had posted on her Instagram account about 20 photos of her enjoying herself at Halloween parties before the slapping incident. Lifestyle portal Shanghaiist reported that her Facebook has been flooded with messages, and some have even demanded to know who her biological mother is.

Ms Leung, who is active on social media, has posted revealing status updates about her emotional state and confrontations with her parents.

In between light-hearted posts about her English bulldog and her idol - singer-turned-fashion designer Victoria Beckham - she also talks about her insomnia and mood swings.

Earlier on Saturday (Oct 31) at about 6.30pm, she put up a cheery post poking fun at her parents.

Then at 7.18pm, she posted that she was "feeling beyond upset" with the status: "I really wanna talk to someone."

Around two hours later, another post of her in Halloween make up appears with the status "Me be stunning. ?#STUNNAAAAH"

In August this year, she posted: "I think I should see a doctor about my clinical weirdness. Like, am I even biologically related to my siblings..??? My parents have always said they adopted me from a bin on the street. Don't think that's a joke anymore."

Ms Leung, who studied mostly in Britain and was last doing a law degree in the London School of Economics and Political Science, also has an older brother and a younger sister.

In March this year, she posted that she was held against her will in Hong Kong's Government House, where her family lives. The posts have since been deleted.

She left home after alleging that her mother had abused her. Mr Leung was forced to give a press conference to deny the allegations. He also said that his daughter was getting treatment for emotional instability.

Ms Leung had told a magazine in Hong Kong earlier that she had a troubled relationship with her parents and had suffered from depression.

In an interview with HK magazine in January, she said of her relationship with her mother: "My mom and I have a complicated relationship. We're similar in the sense that we're aggressive. She expresses it outwardly, but I don't say anything."
In the same interview, she also said that some of her social media posts have been taken too literally.

"People didn't really get the humour behind the joke [on Chai's Facebook profile about taxpayers funding her possessions]. Honestly, what kind of normal person would say 'I'm the Hong Kong princess'? I'm so shocked people believed it. When the whole thing blew up, I thought, 'What?'"

The Chief Executive's Office has yet to issue a statement to confirm or respond to the slapping incident.