The closures in Tamburi, the district of Taranto closest to the plant, were ordered by centre-left Democratic Party mayor Rinaldo Melucci under a new environmental protection plan approved last month by the government.
Regional health officials also advised city residents to keep their windows closed and refrain from sports for the duration of the strong winds sending dust from the plant towards the city.
"We cannot close down the entire city but we needed a symbolic act of protection of the weakest."
But with more than 10,000 employees, Ilva's Taranto plant is also a key component of the local economy and most residents want it to keep operating.
The heavily indebted steel producer, which was effectively nationalised in 2015, is in the process of being taken over by global steel giant ArcelorMittal. But negotiations with the government and unions on the terms of ArcelorMittal's plans to cut costs are currently deadlocked.
Ilva was placed under special administration in 2015 after its former owners, the Riva family, were accused of negligence over toxic emissions.
A huge legal case is ongoing with prosecutors arguing that the emissions led to 11,550 premature deaths over seven years.