At least 29 people suffered minor injuries in an explosion in a busy part of New York that the city's mayor said appeared to be intentional, adding there was no evidence of a "terror connection".

"There is no specific and credible threat against New York City at this point in time from any terror organisation," Mayor Bill de Blasio told a news conference. 

De Blasio said that, though injuries were significant, none of those hurt was likely to die. 

"It is too early to determine what the incident was caused by. We believe it was intentional. A full investigation is under way," the mayor said.

A police official said on Twitter that a second potential device was being investigated.

Al Jazeera's John Terrett, reporting from New York, said police had "found some kind of pressure cooker … wrapped in silver duct tape. It has wires protruding from the centre of it, and on the side of it is some kind of device thought to either be a timer or a cellphone.”

A bomb disposal team was on the scene early on Sunday morning and alert notifications were sent out to cellphones across Manhattan, cautioning those in the vicinity of Manhattan's 27th Street "to move away from the windows," said Terret.

The disposal unit later removed the device from Manhattan for analysis at a specialised facility.

Terret said police had ruled out gas or faulty construction equipment being the cause of the blast.

"They're saying it's not linked to terrorism at the moment but that doesn't mean that it isn't," Terrett said. "It means that they have no evidence and that the investigation continues."

Police spokesman J Peter Donald said on Twitter earlier that the explosion happened at about 8:30pm on Saturday on West 23rd Street in the Chelsea section of Manhattan.

The Chelsea neighbourhood is a residential area popular for its nightlife, and is not near any major tourist sites or government buildings. 

"There's a massive emergency response taking place in downtown Manhattan," Al Jazeera's Kristen Saloomey reported from New York. "The street is blocked off and people are being stopped.

"Witnesses reported hearing a loud bang."

Police combing the area around the scene of an explosion found a pressure cooker nearby connected to a cell phone [EPA]

Source: Al Jazeera News And Agencies