Merseyside Police said the officer was retrieving a backpack filled with cannabis left on Hewitt Avenue when he approached a white Ford Transit van to speak to its occupants, who where acting suspiciously.
When the PC reached into the vehicle to carry out a search under the Misuse of Drugs Act at around 8:15pm the driver drove away, dragging the officer along the road.
The officer sustained a serious injury to his shoulder and wrist, and is receiving treatment in hospital where his condition is described as stable.
A short time later it was reported two men were running from a vehicle into fields near the East Lancs Road, and had discarded a bag.
Two men from Rochdale, aged 26 and 30, were arrested on suspicion of causing grievous bodily harm with intent and the bag and vehicle - which had been left on Ecclesfield Road - were recovered for forensic examination.The 30-year-old was also arrested on suspicion of possession with intent to supply Class A and B drugs (cocaine and cannabis).
Assistant chief constable Paul White said: “Merseyside Police officers put themselves in harm’s way to protect the public from harm every day and understand the risks their role carries.
“They go into dangerous situations involving violent and aggressive offenders day in, day out because they are committed to protecting the people of Merseyside.
“But our officers should never have to tolerate violence against them when they are attempting to carry out their duties.
“Incidents such as this are absolutely unacceptable and have such a massive impact on the officers, their families and colleagues in the force.
“My message to those who carry out violence against police is clear: please remember, whatever you think of us, one day you or your families may need our help too.”
He added: “We have arrested two men, spoken to witnesses and are studying CCTV footage from the area following the incident.
“But we continue to appeal to anyone who may have witnessed any part of it, or who has CCTV or dashcam not yet submitted to police, to come forward.
“Your information or evidence could prove vital as we seek to bring those responsible to justice.”
How to contact police
You can pass on any information via DM @MerPolCC, ‘Merseyside Police Contact Centre’ on Facebook quoting with reference 22000339976. Alternatively, call Crimestoppers anonymously on 0800 555 11