A port strike set to begin across US ports in just hours could cost the American economy between $300m and $5bn per day, according to analysts.

The wide-ranging estimates come as a looming port strike is poised to start as soon as midnight on the US East Coast and Gulf Coast.

That is because a contract between the International Longshoremen’s Association and employers group United States Maritime Alliance expires Monday night amid an impasse over wages and port automation.