Bolton spotted two military-style helicopters flying low. The helicopters even landed at one point, close to the Royal Bolton Hospital, and people took to social media to see what was going on.
Some people shared videos, while others complained about the noise they were causing. One Facebook user commented: "Anyone else seen the two helicopters going over just now.
One with lights on and high up and the other no lights at all and a bit lower very strange, flew over and the one with no lights came back and the one with lights followed it, never known it before." Get daily updates from Bolton direct to your email inbox with the free MyBolton newsletter.Click on this link, enter your email address, and select 'MyBolton News'.
Read more on manchestereveningnews.co.uk