The US health authorities on Friday issued a detailed set of requirements that would allow cruise ships to resume services as early as next month.

The requirements for a "phased resumption" of cruise ship passenger operations were released by the US Centers for Disease Control and Prevention (CDC).

In light of the continued spread of Covid-19, a "careful approach" was needed, the CDC said in releasing its "conditional sailing order."

This would include "simulated voyages to test cruise ship operators' ability to mitigate Covid-19 risk," it said.

"During the initial phases, cruise ship operators must demonstrate adherence to testing, quarantine and isolation, and social distancing requirements to protect crew members while they build the laboratory capacity needed to test crew and future passengers," the CDC said.

Cruises could be no longer than seven days and social distancing would have to be respected during meals.

Cruises were halted in March after Covid-19 outbreaks aboard several ships and a "no-sail" order has been regularly renewed by the CDC. It expires on October 31.

One of the largest cruise operators, Carnival Cruise Line, has already canceled all voyages through November and December except for those between Miami and Port Canaveral in Florida.

Another major operator, Britain's P&O Cruises, does not plan to resume passenger operations before early 2021.