"The situation in Catania and its province is very critical," Regional President Nello Musumeci said.
Two people have died following flash floods in Sicily.
Heavy rainfall flooded streets in the city of Catania on Tuesday, blocked cars and trapped people in their homes.
The office of the regional president, Nello Musumeci, confirmed in a statement on Tuesday evening that "there are already two victims" and that a third person is missing.
The body of a 67-year-old man who was carried away by a flooded river was found in an orange grove in Sicily on Monday. Rescuers are still searching for the man's wife.
Firefighters say the couple's car was dragged two kilometers in two meters of water which had been caused by torrential rains.
"The situation in Catania and its province is very critical," Musumeci said.
All non-essential businesses have been ordered closed until Thursday inclusive to reduce mobility as the area remains under "a state of alert for bad weather."
Planes flying to the Sicilian airports of Catania and Palermo have been diverted to other airports, according to the Italian news agency ANSA.
The mayor of Catania, Salvo Pogliese, has meanwhile closed schools. According to a statement from his office, "in 48 hours the amount of rain that falls on average in an entire year, has fallen on Catania."
Musumeci said in his statement that "eastern Sicily is experiencing a phenomenon that we fear, unfortunately, will be less and less sporadic, with tragic scenarios destined to be repeated."
"Climate change, the fragility of our territory and the condition of instability, often caused by human intervention, are factors that, combined, can have — and we are indeed seeing this — deadly effects," he added.
He stressed that regional authorities have invested over 400 million since 2018 to combat hydrogeological instability and strengthen infrastructure against the risk of landslide and coastal erosion, "but it is not enough, it cannot be enough for a climate that has rapidly tropicised."
"Without extraordinary interventions, which only the European Union can put in place, and without courageous decisions that cannot be postponed by the G20 and COP26, we will periodically find ourselves counting the damage and, God forbid, more victims," he warned.