Mayor Zohran Mamdani acknowledged on Monday that the city did not inform New Yorkers about a partial breakdown of the 911 system last week that prevented hundreds of callers from reaching operators for nearly seven hours.

Pressed on why his administration did not disclose information about the matter, which was made public the evening it happened by The New York Times, Mr. Mamdani replied, “Our first order of business when being alerted as to the issue with the call system was to resolve the call system, and that was the focus.”

“The issue has since been resolved, and the system is running normally,” added Mr. Mamdani, who spoke on Monday during an unrelated news conference.

“Now we are looking to take all the steps that we can to ensure that this does not happen ever again,” he said.

It was the first time that Mr. Mamdani publicly addressed the breakdown, which was caused by a glitch with a software update performed by Motorola, a vendor that provides technology to operate the system, the mayor said. The glitch led to nearly 1,700 calls failing to reach a 911 call center in the Bronx, one of two public safety answering centers in the city.

After accounting for duplicate calls and those made from alarm centers, the Office of Technology and Innovation, the agency that oversees the system’s technology, determined that about 400 people were unable to connect with a 911 dispatcher, according to a City Hall spokesman.

The city tried to reach out to those callers after the outage ended, the mayor said.

Neither Mr. Mamdani nor his spokesman said how many of the 400 people the city reached.

The mayor’s team has said it is investigating the incident, and the City Council plans to hold an oversight hearing next month to press Mr. Mamdani’s administration for answers.

A representative from Motorola did not respond to requests for comment.

The first sign of an issue emerged around 3:15 a.m. last Tuesday, when people dialing 911 could not connect with police emergency operators at the Bronx call center.

The City Hall spokesman declined to answer questions about when the Office of Technology and Innovation first realized there was a problem, and when it notified the Police and Fire Departments.

But, according to emails obtained by the The New York Times, the office issued a memo around 9:30 a.m. after police dispatchers reported a higher number of incoming calls “with no one on the line.” The email said there was “no impact to 911 systems or services.”

About 45 minutes later, the office said the issue had been resolved, according to the spokesman.

But in a second email, sent just before 11 a.m., the office still seemed to be unaware of the impact of the outage. It added that it had rerouted calls to the Brooklyn call center and was investigating the root cause of the issue.

The spokesman declined to comment on whether the system had experienced similar issues in the past, saying, “We are still investigating this incident, and we will provide more information when that investigation concludes.”

Emma Goldberg contributed reporting.