Bruce Berrell of the Calgary Emergency Management Agency said the blast and resulting fire affected fire stations, 911 operations, Alberta Health Services and corporate call centres as well as Shaw's telephone and television services.
He described the building as "a hub of information for a number of clients, not just within the city of Calgary but some of them are provincial and some of them are, in fact, national companies."
He said IBM occupies a couple of floors in the building and their services, too, were affected.
However, he said the scope of the problem had not yet been determined, although it appeared the fire had been extinguished.
"We've activated the municipal emergency plan based on the recommendation of the deputy chief of the fire department," he said.
"Alberta Health Services network is completely dead at the moment. We're trying to determine whether or not the CP Rail information centre (is affected).
"It's a significant network."
The biggest problem was that no one in the downtown core could use a Shaw telephone to contact 911. Berrell said that would be about 30,000 customers.
In the event of an emergency, he recommended people use their cell phones, contact a neighbour or if necessary, go to another location to seek help.
Another problem was in notifying the public of developments in the incident; Berrell noted that an emergency alert had been issued on local television stations but Shaw customers wouldn't be receiving those signals.
He said his department has been sending out tweets and regularly notifying the media.
As for the impact on Alberta Health Services, he stressed that patient care was not being compromised "because there are paper records for all the patients that are in the hospitals. It does impact their data management system that they record the records in."
He said declaring an emergency allows the city to call in the police, emergency crews, Enmax officials and "anybody that can help us with the issues."
"We're trying to get our head around what the actual magnitude of the outage is, and what the impacts are to Calgarians," he said, adding the cause of the explosion is not yet known.
Shortly after the blast, employees were evacuated from the building due to thick smoke.
Fire department spokesman Jayson Doyscher said no one was injured.
The building also houses three radio stations — CHQR, Country 105 and Q107.