Time runs out for Americans in North Korea as travel ban goes into effect For the scores of Americans who live or work in North Korea, time is up.

 -- For the scores of Americans who live or work in North Korea, time is up.

The Trump administration’s ban on travel to the reclusive country went into effect Friday, with limited exemptions available. For the small group of U.S. citizens working on aid projects or at hospitals and universities, their work -- at times, life-saving -- will have to be put on indefinite pause.

That could adversely affect many North Koreans who are dependent on foreign assistance at health centers across the country, according to Heidi Linton, the executive director of Christian Friends of Korea, a nonprofit based in Black Mountain, North Carolina.

“If we’re not able to continue our assistance there, it affects the lives of thousands of patients,” she told ABC News.

Franklin Graham, the well-known Christian evangelist and CEO of the aid organization Samaritan’s Purse, said he agrees.

“No question,” he told ABC News. “And it’s not just the travel ban, it’s sanctions.”

The State Department announced the ban in July, one month after the death of Otto Warmbier, a 22-year-old American student who was imprisoned in North Korea and later died. Warmbier was arrested and imprisoned in North Korea for 17 months, and during his captivity, went into a coma under unknown circumstances. The U.S. secured his release in June, but days after being returned to his parents, he died. Three American citizens are still being held by North Korea.

The ban, which makes it illegal to travel to or through the country with an American passport, does allow for exemptions. Journalists covering North Korea, American Red Cross or International Committee of the Red Cross employees on official business, and other aid workers with “compelling humanitarian considerations” or whose trip is “otherwise in the national interest” are still allowed to travel there. Any U.S. citizen who meets one of those requirements can apply for a waiver, valid for one trip to the country.

The State Department posted application instructions online today -- after the ban went into effect, and weeks after announcing it. A State Department official would not tell ABC News how many people have applied or reached out about obtaining an exemption, citing privacy laws, but the department previously suggested it expects around 100.

The official also would not say how long the approval process will take, but added that even after the department authorizes one’s travel, that person would have to apply for a one-time Special Validation Passport.

Aid workers and university professors, among others, have been scrambling to find out how to apply, and whether they meet the requirements.

Linton, who flew out of Pyongyang on Thursday, said her organization works with around 30 centers in North Korea providing care for patients with tuberculosis, hepatitis B, and other ailments. The group, she said, also facilitates shipments of food, medicine and tractors, supports pediatric care at a hospital, and brings clean, running water to clinics around the country.

“We have 705 patients that have been started on life-saving medicine” for Hepatitis B, she told reporters at the Beijing airport Thursday, “and if they go off that medicine, their lives are in danger. So this, clean water, and many other things, are very important to continue."

On Friday morning, Linton told ABC News that she had not figured out how to apply for an exemption, and said any delay could be disastrous for her group. She said she travels to North Korea four times annually, collectively spending about three months per year there and bringing along eight to 13 Americans on each visit.

“It takes months to really set up these trips,” she said. “If we don't get approval in time, de facto the trip gets canceled, and that sets us back months, and it has direct impact on patients. This work has been built painstakingly over many years, and any disruption in sort of the rhythm and flow of things is extremely disruptive.”

Graham said Samaritan’s Purse, which has worked in North Korea for years, has “been putting everything on hold for right now,” too.

The international aid group has provided food, medical equipment, and more in the impoverished country. Graham said the relief organization had most recently provided six ambulances to North Korea and had received a request for food aid.

“We have our lawyers looking at it, and it’s a little bit of confusion,” he said. “Normally these types of things have gray areas in them, so we’re just trying to figure out what that means for us.”

He said he was confident his group and other humanitarian organizations would be able to get exemptions eventually, but shared the concern for North Korea’s population -- which already faces malnourishment and starvation.

“It’s the people that are down on the street that are just trying to make, you know, ends meet -- the sanctions really hurt those people, and the travel ban,” he said.

The ban will hit North Korea’s only private university particularly hard, too.

Typically, half of the 60-80 foreigners on the Pyongyang University of Science and Technology’s faculty are American, as the size of the faculty fluctuates. Some American staffers bring family members along for their months-long stints teaching North Korean students. But all of the school’s American personnel had left Pyongyang by the end of this week, a university spokesman told ABC News.

With such a depleted faculty, the university will likely open its fall semester, due to begin Monday, in a much-diminished capacity, the spokesman said. The school’s leadership was still figuring out the details, but the ban will likely mean the institution will have to rely heavily on North Korean instructors pulled from local colleges, and primarily offer language classes -- rather than a full slate of disciplines, he said.

As of Thursday, school officials still had not received any guidance from the U.S. government as to how to apply for exemptions, the spokesman said.

They aren’t alone. Tour groups with American guides are also seeking instructions or guidance have not received any word, according to one group.

At one point, American tourists made up the majority of U.S. citizens visiting the country, according to some estimates. Each year, 800 to 1,250 Americans visited North Korea, Koryo Tour Group told ABC News this sping, but that number was declining sharply after Warmbier’s death.

Warmbier was traveling with Young Pioneer Tours when he was imprisoned. Since his death, that company and others like it have stopped serving Americans. Koryo does not let anyone with an American passport even apply to its programs through its online system.

Still, the groups of Americans who have been engaged in North Korea for years stressed that that engagement must continue in order to help solve the ongoing tensions between the two countries.

“This is probably the most dangerous real estate in the world, and the most dangerous government in the world,” Graham said. “We have got to find a way to talk to them and work out our differences because it’s very dangerous if we don’t.”