U.S. authorities now have the power to seize and detain travellers' electronic devices, including laptops and cellphones, and make copies of their contents at an off-site location, under newly disclosed customs policies.

The policy gives border agents at any point of entry into the United States the authority to also take documents, books, pamphlets and hard drives. The items can be seized from anyone crossing the border and may then be copied and shared with other government agencies, according to Department of Homeland Security documents dated July 16.

"Officers may detain documents and electronic devices, or copies thereof, for a reasonable period of time to perform a thorough border search," the policy says. "The search may take place on-site or at an off-site location."

U.S. Senator Russ Feingold told the Washington Post he finds the new policies "alarming" and said he plans to introduce legislation that would make grounds for border searches more rigorous.

Greg Nojeim, senior counsel at the Washington, D.C.-based Center for Democracy and Technology, said the new policies allow authorities to conduct searches without suspicion of wrongdoing.

"They're saying they can rifle through all the information in a traveller's laptop without having a smidgen of evidence that the traveller is breaking the law," he told the Post.

If the authorities find there is not probable cause to hold the seized items, copies must be destroyed, according to the policy. The policy does not outline a timeframe in which materials must be returned.

"These examinations are part of ... long-standing practice and are essential to uncovering vital law-enforcement information," the policy says, noting examinations help authorities detect possible instances of terrorism, narcotics smuggling, child pornography and violations of copyright and trademark laws.