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North Dakota reported a spike in novel coronavirus cases on Saturday after more people tested positive at a wind power factory run by a unit of General Electric, posing a challenge to the state's plan to re-open as early as May 1.

A total of 110 people associated with the LM Wind Power factory in Grand Forks have now tested positive following a screening of about half of its 900 workers this week, North Dakota Governor Doug Burgum told a briefing.

The factory outbreak boosted the number of new cases recorded over the past 24 hours to 90, the largest single day increase, bringing the total number of coronavirus cases in the state to 528. A total of 9 people have died in the state.

Sparsely populated North Dakota remains among the U.S. states least impacted by COVID-19, the disease caused by the highly contagious virus. Only Montana, Alaska and Wyoming have fewer cases, according to a Reuters tally.

While some hot spots like hardest-hit New York have seen their rates of hospitalizations and other numbers start to level off, North Dakota was moving in the opposite direction, Burgum said.

"This is the moment that we expected to happen," he said, noting that the one-day jump was the fourth consecutive record daily high. "We are at that point that we talked about, which is the curve ramping up."

The factory, which makes rotor blades for wind turbines, will be closed for at least two weeks, Burgum said, adding that he issued a stay-at-home order for all its workers regardless of their test results.

A spokesman for General Electric said workers would be paid during the shutdown, and that the company was disinfecting the plant. "We will continue to support our employees and monitor their condition, as we determine when and how we can re-start the plant safely," he said.

Earlier this week Burgum extended lockdown measures in his state through April 30 while outlining requirements to relax those restrictions. At the top of the list were mass testing and contact tracing, the process of identifying people who have interacted with a person with COVID-19 and isolating them to prevent further spread.

Burgum said about 20 officials were working on contact tracing in relation to the factory outbreak, in what he described as a kind of dry run for how the state will respond after re-opening, where officials will investigate cases and isolate contacts so that others can carry on with normal life.

"If you have an outbreak and you want to stay open then we have to do the targeted approach," Burgum said. "We are trying to get more things open, not close more things down."

(Reporting by Nathan Layne in Wilton, Connecticut; Editing by Sonya Hepinstall)