So far 28 people on board the frigate "Panshi" have tested positive for the virus after returning from a trip to the Pacific island nation -- one of just 15 countries that still diplomatically recognise Taipei over Beijing.

"I am the Commander-in-Chief, the military's business is my business and my responsibility," Tsai said in a speech broadcast live.

"There are major shortcomings in the navy's pandemic prevention measures during this mission, and the public is now bearing the risks. I want to give my apologies."

Taiwan has been held up as a model for its swift response to the outbreak, with just 426 confirmed cases and six deaths despite its close proximity and economic ties to China.

It has also won diplomatic praise for shipments of masks and other protective equipment overseas, including to Europe.

The outbreak on the Panshi, however, threatens to undermine the island's impressive track record.

Criticism has mounted in recent days over why the navy pushed ahead with mission despite the pandemic -- and whether officials hid the fact that some sailors were running fevers during the voyage.

The fleet's commander, Rear Admiral Chen Tao-hui, was grilled by lawmakers on Wednesday.

"I swear with my life that I absolutely didn't cover up any infection," he said.

"As soldiers we would rather die at sea, die in the ship. I would not let the virus endanger our countrymen who we should protect," he added.

The ship arrived in Palau on 15 March and left three days later.

The vessel returned to the port of Kaohsiung on 9 April where crew members were allowed to disembark six days later.

The first infections were confirmed over the weekend.

In recent days authorities have raced to track where crew members have been and who may have had contact with them.

Chen and another admiral have been removed from their posts pending further investigation.