Tadley library was temporarily closed on Wednesday afternoon, after three police cars pulled up and detained a man under the Mental Health Act.
A man who did not want to be named said the Mulford's Hill library was closed for most of Wednesday afternoon, during which time, three police cars and an ambulance pulled up.
A notice on the door read: "Due to unforeseen circumstances the library is closed." before the library was re-opened, at around 4pm.
Hampshire Constabulary confirmed officers were called at 12.34pm to assist with a man who was in a vulnerable condition inside the library.
"He was safely detained by police under the Mental Health Act. No injuries were reported and there is no wider risk to the community," said a spokeswoman.