"Having the homicide number come in under 250 will be a great milestone for our department and city, but we can't stop to celebrate," Police Commissioner Charles H. Ramsey said.
Ramsey credited "officers on the ground" for the drop in violence.
"We are proud," he said, "but we still have work to do in our efforts to continue to make Philadelphia safe."
The decrease in violence fits with a trend among the nation's largest cities.
Officials in Chicago and New York City are reporting homicide totals lower than any since the 1960s.
Across the river, Camden's homicide numbers fell, but not as sharply as those in Philadelphia and other cities. Two people were killed Tuesday morning, bringing Camden's 2013 homicide total to 57, down from the record of 67 the year before.
For Philadelphia, for years called the most violent of the nation's largest cities - and long averaging a murder a day - the emphasis now becomes sustaining the drop in killings.
Tuesday night posed special challenges; New Year's Eve is often deadly in Philadelphia.
Two years ago, six people were killed over the New Year's holiday, including a 77-year-old South Philadelphia man stabbed trying to break up a dispute between a family member and a neighbor minutes after the ball dropped.
That marked the deadliest New Year's in Philadelphia in a quarter-century, statistics show.
With a historic low in homicides over the last 12 months, police - as they do each New Year's - concentrated on preventing the celebratory gunfire that sometimes marks the holiday.
On an average night, Philadelphia police receive about 10 reports of shots fired.
Last New Year's between 10 p.m. and 3 a.m., however, police responded to 132 reports of gunfire - the great majority shots aimed skyward.
"Do not fire your guns in the air," Ramsey said at Tuesday's news conference. "What goes up must come down, and you cannot determine where it will fall."
Added District Attorney Seth Williams: "It's a stupid act that can have deadly consequences, and there is nothing festive about it."
Joining Ramsey and Williams was Joe Jaskolka, a South Philadelphia man who remains partly paralyzed since being struck by a stray bullet when, as an 11-year-old boy, he was walking to watch the fireworks at Penn's Landing.
Jaskolka is now 26, and the bullet is still lodged in his head. He has undergone 54 operations.
"This is very simple. What comes up must come down," he said. The shooter has never been found.
Ramsey pleaded for the public to use good judgment. "Ring in the new year in a good way," the commissioner said, "but don't put somebody else's life in jeopardy, because you will go to jail."
Inquirer staff writer Jonathan Lai contributed to this article.