President Joe Biden said his administration has "to do better" to meet COVID-19 testing demands.

During the White House COVID-19 Response Team’s call with the National Governors Association Monday, the president directly addressed the shortages of kits being reported across the nation.

He said the steps the government had taken so far to make more COVID tests available is "not enough."

"If I had known, we would have gone harder, quicker if we could have," Biden said on the call.

He went on, "Seeing how tough it was for some folks to get a test this weekend shows we have more work to do and we’re doing it. We have to do more, we have to do better, and we will."

Dr. Anthony Fauci said a COVID vaccine requirement for domestic air travel should be "seriously" considered.

"If you're talking about requiring vaccination to get on a plane domestically, that is just another one of the requirements that I think is reasonable to consider," he said Monday on MSNBC's "Morning Joe."

"When you make vaccination a requirement, that's another incentive to get more people vaccinated. If you want to do that with domestic flights, I think that's something that seriously should be considered," he said.

This is not the first time that Fauci has argued for vaccine mandates domestic flights.

On Sunday, Fauci told ABC's Jon Karl that "anything that could get people more vaccinated would be welcome."

-ABC News' Arielle Mitropoulos

Mayor Bill de Blasio said New York City has administered more than 180,000 COVID vaccine booster shots since a $100 incentive was announced on Tuesday.

This brings the total number of residents who have received boosters to more than 1.9 million.

"We did a booster incentive and it has been heard and felt by the people of NYC," de Blasio told MSNBC on Monday.

-ABC News' Aaron Katersky

At least four U.S. cruise ships are reporting COVID-19 outbreaks aboard, leading to them being denied entry to -- or turned away from -- foreign ports.

Holland America's Line Koningsdam was denied entry into Puerto Vallarta on Thursday after 21 crew members tested positive.

Additionally, the Carnival Freedom ship was turned away from the Caribbean Islands of Bonaire and Aruba on Wednesday and Thursday, respectively, after "a small number" of passengers aboard tested positive for the virus.

Officials in Aruba and Curacao also turned away Royal Caribbean's Odyssey of the Seas on Wednesday after 55 fully vaccinated crew members and passengers tested positive.

On the same day, passengers aboard the Seven Seas Mariner were not allowed to disembark in Cartagena, Colombia, after six crew members and one passenger tested positive for COVID-19.

Hospitals across England were setting up "Nightingale surge hubs," temporary structures capable of handling 100 patients, as they prepared for a potential wave of omicron patients.

The United Kingdom's National Health Service announced the plan on Thursday, a day after health officials recorded a new daily high for COVD-19 infections.

"Given the high level of COVID-19 infections and increasing hospital admissions, the NHS is now on a war footing," NHS National Medical Director Professor Stephen Powis said in a statement on Thursday.

The NHS said it would start with hubs at eight hospitals around the country. Health Secretary Sajid Javid said in a statement that an additional 4,000 beds could be added if necessary.

“We do not yet know exactly how many of those who catch the virus will need hospital treatment, but given the number of infections we cannot wait to find out before we act and so work is beginning from today to ensure these facilities are in place," Powis said.