They are mainly young men and live in southern states, according to a paper, published in the American Journal of Public Health.

Researchers say these young men tend to have grown up in gun-owning households, are politically conservative (Republican) and own more than one type of firearm. Some of these homes own up to seven different types of weapon.

It comes less than three weeks since gunman killed 56 people and injured more than 500 others in an attack at a Las Vegas music festival.

The massacre was the deadliest in the history of the US, which has the highest rate of murder or manslaughter by firearm in the developed world.

The study, compiled by researchers from the University of Washington School of Public Health, the University of Colorado, the Harvard School of Public Health, and North-eastern University, looked at the handgun-carrying behaviour of 1,444 gun owners using data from a 2015 national survey.

Two-thirds of them said they carried their handguns concealed, while 10 percent did so in an open manner.

The research is the first in more than 20 years to scrutinise how and in what manner US adults carry loaded handguns.

Researchers said state laws on handgun carrying have eased since the 1980s and that some respondents to the survey admitted openly carrying a firearm even in regions where it was illegal.