But Cassano and McAvoy said that before Wednesday, the fire department and Con Ed had received no complaints in the last 30 days about a gas leak in the area.
NYPD spokesman Stephen Davis said detectives have interviewed the landlords of both buildings to help identify occupants and tenants, but he didn't immediately know if they'd been interviewed about reports of gas leaks by tenants.
An Associated Press analysis of the city's 311 calls database from Jan. 1, 2013, through Tuesday also found no calls from the buildings about gas.
The lesson, De Blasio said, is that because of the city's old and vulnerable infrastructure, people should heed the post-Sept. 11, 2001, slogan, "If you see something, say something."
Sumwalt said the NTSB would be checking calls to the city's 911 emergency line and 311 information line and interviewing witnesses, first responders, the injured and those who smelled gas.
The working-class neighborhood around the site was once known as Spanish Harlem because of its large population of Puerto Ricans but now has many Asians and other ethnic groups. The neighborhood is gentrifying but still has a high crime rate, fueled by drugs and gangs.
Storefronts range from fast-food shops to botanicas selling folk medicine and religious items.
More than 30,000 miles of decades-old, decaying cast-iron pipe are still being used to deliver gas nationwide, according to the U.S. Transportation Department estimates. In 2011, the American Gas Association said replacement or repair could cost $82 billion.
New York City still uses about 3,000 miles of old cast iron, Boston about 2,000 miles, Philadelphia about 1,500 and Washington 400, the department said. Experts said much of the pipe dates to before World War II, and some of it may even be more than 100 years old.
Associated Press writers Jake Pearson, Ken Sweet, Julie Walker, Jonathan Lemire, David B. Caruso, David Crary, Leanne Italie, Karen Matthews, Deepti Hajela, Jim Fitzgerald, Mike Casey and Sonia Moghe contributed to this report.