New York City experienced a 10-day stretch in February without any murders and had one day -- March 5 -- without any murders, shootings, stabbings or slashings, heartening evidence of improvements on already-low crime rates, Mayor Bill de Blasio and NYPD Commissioner William Bratton said Tuesday.

Overall, major crime is down 2 percent compared with this point last year, homicides are down 21 percent and shootings are down 14 percent, de Blasio said at a City Hall news conference.

"This is becoming an incredibly safe city," Bratton said, adding that the 10-day period and March 5 were firsts since the NYPD began keeping records.

He pledged to improve the numbers even more going forward: "The bottom is zero."

De Blasio credited Bratton for having "driven down already historically low levels of crime" in the pair's first 10 weeks in office through a "spirit of collaboration."

"Under Commissioner Bratton's leadership, the NYPD has shown that it is able to keep reducing crime while dialing back the tensions that have too long marred the relationship between the police and the community," the mayor said.

Bratton said the cold weather may be just one of several factors in the low crime rates.

"Jack Frost is a best friend of a police officer," he said.

Bratton said his department will "find even better and more humane and more successful ways" to fight crime.

De Blasio's news conference Tuesday served to announce four appointments to criminal justice posts in his administration.

Joseph Ponte will be commissioner of the Department of Correction; Ana Bermúdez will be commissioner of the Department of Probation; Elizabeth Glazer will be director of the Mayor's Office of Criminal Justice; and Vincent Schiraldi will be senior adviser to the criminal justice office.