A man is being questioned about an attack on a frontline healthcare worker who was punched in the head while working at a COVID-19 testing site in Sydney’s north-west.

Deputy Police Commissioner Gary Worboys said the unmasked man “pushed a telephone into her face, dislodged her mask, then struck her in the face” on Monday afternoon when she was working at the Dundas COVID clinic.

He “said some horrible things” about vaccinations before fleeing when other people waiting to be tested jumped out of their cars to help the 31-year-old woman.

“The behaviour is totally unacceptable. No one, no one, would say that there is any reason to behave like that to any person let alone someone that is out there every single day helping us to get through what is a very challenging situation with the pandemic,” he said on Wednesday.

Police released images of a man they wanted to question about the attack and Mr Worboys said a man was now in custody.