A total of 571 new cases of the virus were recorded in the latest 24-hour reporting period.
Three people have died and over 10 percent of the population in the capital Majuro have tested positive according to the Marshall Islands Ministry of Health and Human Services.
The WHO has declared the outbreak as a Public Health Emergency of International Concern.
All schools will be closed for the next two months, just one of the measures under the government's disaster management plan.
The number of positive cases has skyrocketed from a handful on August 8 to over 1000 by the weekend.
RNZ Pacific's Marshall Islands correspondent Giff Johnson said the outbreak has led to staff shortages at many businesses.
"Everybody's operation is affected. I went next door to buy some drinks and the owner is doing the cash register ... all cashiers are out of action with Covid. The post office had to close down because so many people came down with Covid."
Photo Red Cross Marshall Islands