- Several people were reportedly injured after blast in midtown Manhattan
- Police sources said pipe bomb was detonated at Port Authority
- Eye witnesses said, "There was a stampede up the stairs to get out"
Police were not yet identifying the device used. Local television channel WABC cited police sources as saying a possible pipe bomb detonated in a passageway below ground and WPIX cited sources as saying a man with a "possible second device" has been detained in the subway tunnel.
The fire department tweeted there were four injuries, all non-life threatening. One of the injured was a Port Authority police officer.
The bus terminal was temporarily closed, the Port Authority of New York and New Jersey said in a Twitter statement.
A large swathe of midtown Manhattan was closed to traffic, between 45th Street to 40th Street and 7th Avenue to 9th Avenue, police said. Subway trains were bypassing the Times Square station, the city's busiest.
New York City Mayor Bill de Blasio and President Donald Trump have been briefed on the incident. New York governor Andrew Cuomo was on the scene.
First reports of the incident began soon after 7 a.m. (1200 GMT), at the start of the city's rush hour. New York in December sees a surge of visitors who come to see elaborate store displays, the Rockefeller Center Christmas tree and Broadway shows.
News of the incident jarred financial markets as trading was getting underway for the week. Standard & Poor's 500 index emini futures pared gains, the dollar weakened against the yen and U.S. Treasury securities prices gained on a modest flight-to-safety bid.
The incident occurred less than two months after an Uzbek immigrant killed eight people by speeding a rental truck down a New York City bike path, in an attack for which Islamic State claimed responsibility.
In September 2016, a man injured more than two dozen people when he set off a homemade bomb in New York's Chelsea district.