A bomb that exploded in New York City was an act of terrorism, Governor Andrew Cuomo says, but no link to international groups has been found, The Associated Press reported.

Cuomo said significant damage had been caused and "we were lucky there were no fatalities". Saturday night's blast in Manhattan injured 29 people. Some 1,000 extra security personnel are being deployed to transport hubs.

"Whoever placed these bombs - we will find them and they will be brought to justice," Cuomo said.