A man has been arrested after he allegedly sexually assaulted a child in a public toilet and stabbed another man in Sydney’s south.

It’s believed the 54-year-old man assaulted and sexually assaulted the seven-year-old girl in the toilet of the St George Dance Studio on Railway Parade in Kogarah about 7.55pm on Thursday.

A 46-year-old man who confronted the alleged offender was stabbed in the abdomen and neck during a struggle. Bystanders came to the injured man’s aid and detained the offender until police arrived.

The 46-year-old was taken to St George hospital in a stable condition. The girl was taken to Sydney Children’s hospital for observation.

The 54-year-old was arrested and taken to hospital with facial swelling and bruising. He remains under police guard and will be interviewed later on Friday.

Mo Hariri, from Hariri Chicken across the road, heard the commotion and came outside.

“Someone came out and yelled ‘call the police he’s trying to kill him’,” Hariri said.

He also heard someone yell: “Where’s my daughter?”.

Later, the man who had been stabbed came down the stairs bleeding and Hariri’s friend gave him resuscitation and covered his multiple wounds.

Hariri described the weapon used to stab the man as a scalpel.

NSW Police Superintendent Julian Griffiths said the alleged offender – from Kogarah – was not a staff member or known to the dance studio.

“Investigators have not been able to identify he has any links to those commercial premises and it appears to be a random, isolated incident,” he told reporters in Sydney.