(NEXSTAR) — The number of infected sailors on a South Korean destroyer on an anti-piracy mission off East Africa has soared to 247, the largest cluster for the country’s military during the coronavirus pandemic.

The Defense Ministry said Monday two military aircraft have been sent to bring back all 301 sailors aboard the destroyer Munmu the Great.

Authorities suspect the outbreak may have started when the destroyer docked in the region to load goods in late June. None of the crew has been vaccinated against the coronavirus.

Health officials have said the crew are all in relatively good condition.

Home to roughly 52 million people, South Korea has fared better than many countries during the pandemic, but is now seeing a sharp rise in cases.

On Monday, the country reported 1,252 new coronavirus cases. It was the 13th straight day for South Korea to register more than 1,000 new cases.

Just about 11 percent of residents are fully vaccinated and fears over the sudden spike in positive tests prompted a rush for available doses last week, crashing the official reservation website, Reuters reported.

As of Monday, South Korea had recorded 179,203 COVID-19 cases and 2,058 deaths from the virus, according to Johns Hopkins data.

The Associated Press contributed to this report.