Two men have been charged following an alleged street fight and police pursuit in Sydney's west early on Friday morning.
But two other men - dubbed "dangerous cowards" by senior NSW Police - remain at large as the constable recovers in hospital.
A third remains in custody.
The overnight attack at Doonside in the city's west followed a police pursuit of a car with four men and an earlier street fight with a fifth man.
Three people were arrested, including the 20-year-old who allegedly lashed out with a large knife and machete.
The constable, 34, suffered slashes under his ribs and on his back.
"The conduct is abhorrent," NSW Police Assistant Commissioner Gavin Wood said.
"I can't mix words here ... sometimes you think you've seen it all, but for a young police officer to be out at one (o'clock) in the morning looking after the community ... then suddenly he's in hospital with two significant stab wounds."
More than half a dozen machetes and knives, most measuring about 30 centimetres, were allegedly found on the arrested trio.
Mr Wood denied any potential confusion about the fact the police officer was a constable, despite the man and his partner being in plain clothes.
Each had police identification and stepped out of a car that was clearly an official vehicle, he said.
Despite the constable being stabbed, he and his partner "collectively effected the arrest" of the 20-year-old, Mr Wood added.
The wounded man was treated by paramedics and taken to Westmead Hospital, where he remains in a stable condition.
One wound was yet to be stitched up eight hours after the attack.
The incident occurred after police pursued a hatchback carrying four men who were allegedly involved in a fight in the same suburb.
A fifth man was seen running from the scene of the fight, police said.
The hatchback later crashed into a power pole and the men fled on foot.
Two people remain at large.
"These men are cowards, dangerous cowards," Mr Wood said of the remaining pair.
"We are coming after them, as we speak."
The 20-year-old has been charged with reckless wounding of a police officer, which carries a maximum 12-year jail term, among other offences.
He was due to appear in Blacktown Local Court later on Friday.
An 18-year-old was also due to face the same court charged with being armed with intent to commit an indictable offence, being in custody of a knife in public and other offences.
He was arrested at Plumpton, as was a 21-year-old man, who is yet to be charged.
The arrested trio had some links to gang crime, police said.
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