Police had begun removing the cordon and workers were slowly being allowed back into site, he said.
Earlier on Tuesday a separate Reuters witness reported scores of people running from the Arndale shopping centre, with some saying they had heard a big bang.
At least 22 people, including some children, were killed and 59 were wounded when a suicide bomber struck as thousands of fans streamed out of a concert by U.S. singer Ariana Grande in the English city of Manchester on Monday.
(Reporting by Michael Holden, writing by David Milliken, editing by Paul Sandle)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)