UPDATE - 29 injured in NYC explosion

ADDS DETAILS FROM PRESSER, UPDATES THROUGHOUT

NEW YORK (AA) – Twenty-nine people were injured in an outdoor explosion late Saturday in New York City, Mayor Bill de Blasio told reporters.

One injury resulting from the explosion at around 8.30 p.m. (1230 GMT) at 131 West 23rd Street in the Chelsea neighborhood of Manhattan "might be considered serious", de Blasio said.

The cause remains unknown.

Authorities believe it was intentional but have not found any link to terrorism, he said.

Republican presidential candidate Donald Trump reacted to the incident during a rally in Colorado, calling it a "bomb".

"I must tell you that, just before I got off the plane, a bomb went off in New York and no one knows exactly what's going on," Trump said. "We've got to get very, very tough," he added.

His rival, Hillary Clinton, did not comment but her campaign said she was informed of the developments.

Clinton and Trump live in New York.

Police officers are treating the nearby 27th Street between the 6th and 7th avenues as a second site, declining to give further details.

There is intense police activity in the area, with closures on nearby roads and subway stops.

Officials said there was no immediate connection between the Chelsea blast and a pipe bomb explosion in Seaside Park, New Jersey, earlier Saturday, which forced the cancellation of a charity run.

That blast caused no casualties.