LONDON — The police in Manchester, England, were investigating a shooting that injured at least 10 people early Sunday in the Moss Side area as “an attempted murder,” and officers were working on the premise that a shotgun had been used, an official said.

The shooting unfolded in the predawn hours, shortly after revelers attended the first day of an annual Caribbean carnival in the area.

“It is unclear at this stage what the motive, what the reason behind this attack, was,” the chief superintendent of the Greater Manchester Police, Wasim Chaudhry, said at a news conference Sunday afternoon.

“However, we’ve got to be clear, it would be obvious to any particular person that discharging a firearm in a large crowd like this is completely reckless,” he said.