Everyone who works at City Hall — including the press corps — is being offered training on how to respond if an “active shooter” penetrates the historic building.

The mayor’s office said the voluntary training is precautionary and “there are no current threats” against either Mayor Bill de Blasio or any government buildings.

But City Hall shootings aren’t unprecedented.

The drill comes just three days before the 15-year-anniversary of the shooting of Councilman James Davis inside the second-floor council chambers in 2003.

Davis was killed when he invited a political opponent to City Hall and escorted him past the metal detectors. As both men were sitting in the balcony during a council hearing, the rival pulled a gun and killed Davis.

A police officer, in a remarkable feat of marksmanship, fired a single shot from the floor of the council chambers to take out the shooter without anyone else getting injured.

Friday’s training will teach employees what to do if a cop isn’t around to help.

Staffers will learn to evacuate, hide or act if they can’t flee or take cover – similar to FEMA’s “run, hide, fight” protocol.

A City Hall spokeswoman said the training was not prompted by a specific incident, and that the NYPD offers the training regularly year-round at city agencies and businesses.

“Safety is our top priority, and we’re offering this voluntary training out of an abundance of caution to ensure employees are prepared in the event of an active shooter,” Olivia Lapeyrolerie said.

In the age of regular mass attacks, active shooter training is becoming the norm in schools and workplaces.

An initiative in San Antonio called the Texas School Marshal Program, even trains school staffers how to intervene with their own guns.