Mayor Bill de Blasio Wednesday said he is prepared to "start over" on a 911 system overhaul that is currently five years behind schedule and about $1 billion over budget.

His administration on Sunday ordered a halt on work that began under former Mayor Michael Bloomberg to improve the existing 911 system by making it more sophisticated and better integrated with city agencies. De Blasio's team also began a 60-day review of the cost overruns, delays and technical problems.

The probe will determine whether the system can be improved and "if that can be done in real time, in a cost-efficient manner, under the current rubric -- or alternatively, if we, bluntly, have to start over, and find, you know, other firms, other expertise to get this done properly," de Blasio said Wednesday in the Bronx.

He said it is "absolutely" safe for New Yorkers to depend on the existing 911 system while the review is conducted.

The project began in 2004 as a five-year, $1.3 billion initiative.