Dr. Francis Collins, the director of the National Institutes of Health, is urging Americans to be vigilant in the wake of a new variant of the novel coronavirus that is sweeping the globe.

The World Health Organization has designated omicron as a "variant of concern." But so much remains unknown about omicron, including whether it causes severe disease and if it is more contagious than delta, which is currently the dominant variant in the United States.

"We're collecting that information as rapidly as we can, and much credit to our colleagues in South Africa who have been totally transparent about this. We only learned about this one week ago from one of their sequencers," Collins told ABC News' Robin Roberts in an interview Tuesday on "Good Morning America."

"So we are quickly trying to figure out in South Africa, is this in fact more contagious than other variants? It does look like it's spreading quite quickly there," he added. "But we don't know how that would play out in a country like ours, where delta is already so dominant. Would omicron be able to compete with delta? We don't know the answer to that."

Another big question, Collins said, is whether the current COVID-19 vaccines and boosters will provide protection against omicron as they have against previous variants. The answers will "take a couple of weeks" to uncover, he said.

In the meantime, Collins encouraged all Americans to get vaccinated and boosted if eligible, and to wear face masks.

"I wear my mask if I'm indoors with other people -- I don't always know if they're all vaccinated or not. That's just good practice," he said. "I know we're all tired of this, but the virus is not tired of us and it's continuing to exploit those opportunities where we're careless."

Dutch health authorities announced Tuesday that they have detected omicron in two previously tested samples, dating back as much as 11 days, indicating that the new variant was already circulating in western Europe before it was first identified in southern Africa.

The Netherlands' National Institute for Public Health and the Environment said it discovered omicron in samples dated Nov. 19 and Nov. 23, preceding the cases found among people traveling from South Africa to the Amsterdam Airport Schiphol on Nov. 26.

"It is not yet clear whether these people had also visited southern Africa," the institute said in a statement Tuesday.

Out of 624 passengers returning from South Africa who were tested for COVID-19 at the Amsterdam Airport Schiphol on Nov. 26, 61 tested positive, including 14 with the omicron variant.

"Laboratory tests identified several different strains of the omicron variant," the institute said. "This means that the people were very probably infected independently from each other, from different sources and in different locations."

The omicron variant was first reported to World Health Organization from South Africa on Nov. 24.

One of the South African scientists who helped identify the omicron variant took to Twitter to slam the travel bans imposed on southern African countries as a result of their discovery.

Tulio de Oliveira, director of the Center for Epidemic Response and Innovation in Stellenbosch, South Africa, tweeted Monday night that he had "spent a big part" of his day speaking with genomic and biotech companies because "soon" his team "will run out of reagents as airplanes are not flying to South Africa."

In a series of tweets last week, de Oliveira urged the world to "provide support to South Africa and Africa and not discriminate or isolate it."

"We have been very transparent with scientific information. We identified, made data public, and raised the alarm as the infections are just increasing. We did this to protect our country and the world in spite of potentially suffering massive discrimination," he tweeted.

"This new variant is really worrisome at the mutational level. South Africa and Africa will need support (financially, public health, scientific) to control it so it does not spread in the world. Our poor and deprived population can not be in lockdown without financial support," he said in another tweet.

De Oliveira, who is leading a team of scientists analyzing the genomic sequencing of the new variant, issued an appeal to billionaires and financial institutions to support South Africa and the African continent.

"We do have funding for science, but South Africa and Africa need financial help to support their deprived population and health system," he tweeted. "By protecting its poor and oppressed population we will protect the world."

Japan confirmed on Tuesday its first case of the omicron variant, according to Chief Cabinet Secretary Hirokazu Matsuno.

Matsuno told a press conference that the patient is a man in his 30s who tested positive for COVID-19 upon arrival at Japan's Narita International Airport on Sunday after traveling from Namibia. A genome analysis confirmed Tuesday that he was infected with the new variant, which was first identified in southern Africa last week.

The man was isolated and is being treated at a hospital, according to Matsuno, who refused to disclose the patient's nationality. His travel companions and the passengers who sat nearby have been identified and referred to Japanese health authorities, Matsuno said.

Earlier this week, Japan announced that it will ban all foreign visitors starting Tuesday as an emergency precaution against omicron, which the World Health Organization has classified as a "variant of concern." The government is also requiring Japanese nationals and foreigners with resident permits to quarantine 14 days upon entry.

-ABC News' Anthony Trotter