In signing the bills, Bloomberg turned away criticism from some retailers that the measures would be economically harmful and lead to job losses.
"This is an issue of whether we are going to kill people," Bloomberg said. People who raise the economic argument, he said, "really ought to look in the mirror and be ashamed."
The ban has limitations, in terms of its ability to stop young people from picking up the deadly habit. Teenagers can still possess tobacco legally. Kids will still be able to steal cigarettes from their parents, bum them from friends or buy them from the black-market dealers who are common in many neighborhoods.
But City Health Commissioner Thomas Farley said the idea is to make it more inconvenient for young people to get started, especially young teens who had previously had easy access to cigarettes through slightly older peers.
"Right now, an 18-year-old can buy for a 16-year-old," he said. Once the law takes effect, in 180 days, Farley said, that 16-year-old would "have to find someone in college or out in the workforce."
Tobacco companies and some retailers had opposed the age increase, saying it would simply drive teenagers to the city's thriving black market.
"What are you really accomplishing? It's not like they are going to quit smoking. Why? Because there are so many other places they can buy cigarettes," said Jim Calvin, president of the New York Association of Convenience Stores. "Every 18-year-old who walks out of a convenience store is just going to go to the guy in the white van on the corner."
Large cigarette companies now commonly offer merchants incentives to run price promotions to bring in new customers. Those discounts, though, will be banned by the new law, which aims to keep the price of cigarettes high as a way of deterring smokers. The city already has the nation's highest cigarette taxes.
Calvin said the elimination of discounts would further feed the drift away from legal cigarettes, and toward illicit supplies brought into the city by dealers who buy them at greatly reduced prices in other states, where tobacco taxes are low.
Both bills were passed by the City Council late last month. The legislation also prohibits the sale of small cigars in packages of less than 20 and increases penalties for retailers that violate sales regulations.