There were hundreds of people on the train at the time, early on Thursday, many of them commuting for work.
The train was travelling between Cremona, in the Lombardy region, towards Milan’s Garibaldi station.
It derailed at the Pioltello Limito station on the outskirts of Milan at about 7am, emergency services said.
Two centre carriages came off the rails, coming to rest at an angle.
The field beside the railway lines is filled with rescue vehicles, Italian news outlet ANSA reported.
Rescue workers have been climbing through the carriages helping passengers to escape.
Cristina Corbetta, an official with the regional emergency services in Milan, told Sky TG24 that about 100 people had suffered minor injuries and 10 had been seriously hurt.
Five or six people are still trapped inside, according to the TV station.
The cause of the derailment is not yet clear.
The last major train crash in Italy was in 2016, when 23 people were killed in a two-train collision in Puglia, southeastern Italy.
More from World
North Korea calls for reunification with South Korea
China clones two monkeys in world first
Logan Paul back on YouTube with suicide prevention video
Google calls time on race to reach the moon
Larry Nassar: Disgraced Olympic doctor sentenced to 175 years for abusing gymnasts
Sentencing of Larry Nassar: Testimonies of ex-USA Gymnastics team doctor’s accusers
In 2009, 32 people were killed when a freight train carrying liquefied petroleum gas derailed and exploded in Tuscany.