Parking bans also are in place, road closures are on the way, and now, officials are securing the site of the two-day summit, which begins Sunday.
More barriers are expected to go up Wednesday night. They will eventually form a perimeter stretching from 21st Street south to 25th and Indiana east to the Lake.
"The fence of course will make it difficult for people to get through," said Jody Weis, former Chicago Police superintendent. "But you've got to supplement that with officers and other people standing guard with the fence."
In addition to the fences, concrete barriers -- some stationary and some portable -- will reportedly be used to guard against large scale explosives.
"I'm sure we're going to see more and more levels of security, keeping in mind that a large vehicle bomb is incredibly dangerous to the people that are coming into town for this event," Weis said.
It's not just at McCormick Place where defenses are going up. Several Michigan Avenue buildings in the South Loop have now covered their windows with plywood, despite the discouragement of the NATO host committee which wants the city to appear as welcoming as possible.
"I think it's a little extreme," said Abbie Torgeson, South Loop resident. "I really don't think that anyone down here in the south loop expected any businesses to do anything like this."
In addition to boarding up, crews at an apartment building at Michigan and 21st were installing bullet proof glass at the cost of nearly $400 per window pane.
Steven Trzaskowski, of Buzy Bee Board Up, doesn't think it's an overreaction. "I think it's more about protection and the safety of residents in a building like this," he said.
At Boeing headquarters in the West Loop where on Monday Occupy Chicago is planning a rally to shut down the building, crews Tuesday night added anti-shatter materials to the large street side windows.
At a condo high-rise at 14th and Michigan, the all-glass canopy was covered in bubble wrap.
"Just in case something fell on it or was thrown on top of it, we didn't want glass shattering on anyone," said Judy Pierson, property manager, 1400 Museum Park.