After 8 a.m. (local time), a team of firefighters followed by a group of plainclothes police officials entered the campus, Efe news reported.
They were looking for Molotov cocktails, chemical products and possible explosive devices, as well as any students who may still be hiding.
Over the past two days, civilian search teams have combed the campus in search of around 20 radical activists believed to remain blockaded inside, but found no one.
However, EFE was able to verify the presence of at least one student who said he was hiding with other young people for fear of police reprisals, although the police have said that if they find someone, they will allow them to leave without arresting them.
The student told EFE he has no faith in the police.
Police superintendent Lau Sin Hon told EFE that the police intended to split into teams of 10 to inspect the campus.
As soon as they finish the search and confirm that there is nothing dangerous inside, they will hand over the campus to the university authorities, he added.
The campus has become one of the iconic sites of the pro-democracy demonstrations being carried out by thousands of people in the city for months, and was turned into a battleground.
Walls painted with phrases such as "Free Hong Kong," remnants of fires, barricades made from furniture, a trail of molotov cocktails, masks and helmets, and student slippers and backpacks are all now found on the campus.
After fencing off the PolyU campus, authorities stormed the premises on November 18 and a battle broke out that ended with more than 1,000 arrests, including 300 minors, and dozens injured.
About 100 students fought back and managed to barricade themselves inside the campus.
Over time many surrendered or escaped.
Even so, it is thought that around 20 protesters remain inside divided into smaller groups on the upper floors to avoid detection.
( With inputs from IANS )