Shellharbour's Daniel Mansbridge is used to helping others in dire straits but on Friday it was he who need to rely on the skills of colleagues after he was brutally attacked on Windang bridge while riding his bike to raise money for charity.

Mr Mansbridge was only seven kilometres into his ride when he came across a group of about 10 teens on the bridge.

Read more: Off-duty paramedic bashed at Windang while on charity bike ride

One boy, aged about 12-years-old, was "showing off" to his mates when he yelled and knocked Mr Mansbridge, sending him flying over the handle bars.

After shaking himself off, the off-duty Oak Flats paramedic approached the group, wanting to tell the boy how silly he had been, however was set upon by two of the teen's mates.

He suffered a fractured eye socket along with swelling and scratches to his face in the ordeal.

However, Mr Mansbridge said he is not angry.

"I would like the teens to learn a lesson in tolerance," he said.

"We all make mistakes. They just need to be aware of the consequences of their actions.

"I could have ended up over the rail and in the path of oncoming traffic."

After the boys stopped punching him, Mr Mansbridge told the group he just wanted to talk, which made them realise they had "gone too far". They apologised and collected his bike and belongings.

"I was just thinking 'bloody hell, this isn't good'," he recalls of the attack.

"I was shocked. I didn't know what to do. They were kids. There was no way I was going to hit them."

Mr Mansbridge called a colleague who picked him up and took him to Shellharbour Hospital for treatment.

NSW Ambulance Chief Inspector Terry Morrow said it was "distressing" to hear one of his colleagues had been attacked.

"We are really proud of Daniel and other people who are in our service who are out there riding [for a cause] and then all of a sudden to have one of our officers randomly hit...we are appalled by the whole situation," he said.

"We have all, at various stages, have been involved in assaults which is not good.

"Daniel is the sort of character...who is out there to help not harm people.

"We are quite upset by this occasion, he is one of our own and we are trying to look after him."

Lake Illawarra police are investigating the incident.

Mr Mansbridge will be off work for about a month after he has surgery to fix his fractured eye socket.

He feels "overwhelmed and humbled" by the support from his NSW Ambulance colleagues and people on Facebook after a post about the attack went viral.

He plans to get back on the bike and complete the Great Cycle Challenge for the Kids Cancer Charity.

He wants to finish riding 1000km and hopes to continue to raise money. All funds raised from a GoFundMe page with go to the charity.