NEW YORK-AFP - New York raised the minimum age to buy cigarettes to 21 on Sunday, in its latest initiative to encourage healthier behavior among residents.

The law, signed November 19 shortly before former mayor Michael Bloomberg finished let office, had a six-month waiting period before it came into effect -- but its impact can already be clearly felt.

"Under 21, no tobacco," warned a small sign at the entrance of a small shop that sells smokes, newspapers, candy, coffee and cakes, in the Nolita neighborhood (North of Little Italy).

No tobacco, either, for anyone who can't present a valid ID proving their age. Shopkeeper scan IDs to test their authenticity before handing over the box of cigarettes.

The measure -- unprecedented among America's big cities -- raises the legal age to buy cigarettes from 18. It also applies to other forms of tobacco and to e-cigarettes.

It's the latest of New York's efforts to reduce smoking in the city, which bans cigarettes and, as of April 29, e-cigarettes in restaurants and bars, in parks or squares, and at the city's public beaches. Some private residential buildings have also banned smoking.

Cigarette taxes in the city are also the highest in the country: $5.85 a carton, which brings the overall price to around $12. In addition, the city has established a minimum price of $10.50 a box for cigarettes.

Nataleigh Kohn, 23, who works at a startup company, underwent her ID check with good grace.

"It is a good thing. People in high school can't start smoking," she said.

Thomas Wall, 24, a former smoker who works in architecture, agreed, though he said the measure probably wouldn't eliminate teen smoking all together.

He compared the new age restriction to the ones around alcohol, which set the US drinking at at 21.

When underage people want alcoholic drinks, they often get them from older people who buy for them.

Shopkeeper Muhammad Arisur Khaman said he's seen some complaints since the law was implemented, but not many. He just tells unhappy clients: "It's the law."

The higher minimum age is "a step in the right direction," said Pat Bonadies, a teacher walking with a group of students in Union Square.

The 52-year-old said there has been a sea change in attitudes towards smoking.

"When I was younger, smoking was much more prevalent among teenagers and preteens in restaurants and social settings," she said.

"Even my mother's friends, they smoked during their pregnancies."

The city has seen a sharp drop in adult smokers, from 21.5 percent in 2002 to 14.8 percent in 2011, according to official statistics.

But the smoking rate among young people has been steady since 2007, at 8.5 percent, which was part of the impetus for raising the minimum age.

Authorities hope that the new law will cut the smoking rate among 18 to 20 years by more than half.

New York hopes to inspire other cities to pass similar age restrictions.