North Wales Fire and Rescue Service responded to reports of a fire and smoke at an aluminium works at London Road, Holyhead, at 03:29 BST.
The A55 was closed for a short time between J1 A5 Victoria Road and London Road and J3 A5 (Valley) due to concerns about a risk of further explosions, said North Wales Police.
One fire crew remains at the scene.
Multiple agencies attended the site and, after checks, it was declared safe and roads were reopened, a police spokesman said.
Fire crews have been called to several reports of an explosion at Anglesey.