Up to six people then allegedly joined in, punching and kicking the constables.
The source told the Herald that the bouncer then stepped in and rescued the pair.
Had he not been there, the constables could have suffered life threatening injuries.
"This is a regular occurrence on Christmas Eve as people go partying ... If it wasn't for the bouncer from the bar, both officers would have been in serious trouble," a second source said.
It is understood the injured officers are on leave and will not return to work until they are medically cleared. Both sustained wrist fractures and cuts and bruises.
Two people were arrested and charged in relation to the brutal attack.
Jez Cameron, joint owner of the Orewa bar, refused to comment on the incident.
Police Association spokesman Luke Shadbolt said the attack was unacceptable.
"It is all too frequent at this time of year," he said.
"The reality is, a lot of police are assaulted. They have to be out doing their job and making sure people are drinking responsibly and getting home safely ... It is a real shame when our colleagues are assaulting trying to make people safe."
He said Christmas and New Year were peak times for police to be assaulted.
"It often happens in smaller holiday areas where populations swell ... people often drink more and behave differently there than they would in their home environment. It is a regular occurrence, usually New Year's Eve is the one - if something is going to happen, it will happen that night."
The attack came just a day after Auckland City Inspector Kerry Watson was assaulted by a man he had pulled over.
Inspector Watson was repeatedly punched in the face and head after he stopped a vehicle being driven with no headlights in Mangere.
A 45-year-old man has been charged with aggravated assault, driving while disqualified, escaping custody, threatening behaviour and refusing a request for a blood sample.