The state PBA is offering a $20,000 reward for information on whoever knocked out a Long Branch police officer who was trying to make an arrest early Tuesday.

Officer Mike Monahan suffered a concussion when someone hit him in the back of the head around 2 a.m. after he chased down a suspect in an abandoned nursing home along Bath Avenue, police say.

Backup officers arrived and found Monahan unconscious after he failed to answer radio calls.

They say Monahan spotted several people in the building and gave chase, eventually catching up with one of them, who he was attempting to arrest when the attack happened.

Neighbors say the abandoned building has become a dumping ground for trash, including old mattresses, tires and TVs. According to some, there is at least one squatter living inside. The community there wants the property's owners to address those problems.

While News 12 was on the scene, workers placed plywood over one of the doors to help keep people out of the building. News 12 attempted to contact the landowner but did not receive a response from someone who could answer questions.

The injured officer was expected to be released from the hospital sometime Wednesday after being treated for a concussion.