NEW YORK — Fifteen COVID-19 vaccination hubs run by New York City are postponing all first-dose appointments and other sites have stopped making new appointments as the state burns through its supply of the shots, officials said Thursday.

Vaccinations in the city haven't stopped, Mayor Bill de Blasio said. Another 45,000 doses were administered Wednesday, bringing the total number of people who have gotten a shot in the city to nearly half a million.

But the city's capacity to hand out shots, which was initially limited, now far exceeds the number of doses available.

"We're going to be at 50,000 a day and more very soon if we have the vaccine to go with it," de Blasio said. "It's just tremendously sad that we have so many people who want the vaccine and so much ability to give the vaccine, what's happening? For lack of supply, we're actually having to cancel appointments."

De Blasio and New York Gov. Andrew Cuomo, who are both Democrats, have been pleading for more doses of the two vaccines that have been approved for emergency use. Both require two doses for maximum effectiveness.

In the meantime, all Jan. 21 through Jan. 24 appointments for the first dose of the vaccine at 15 community vaccination hubs set up by the city health department have been postponed to next week.

Other health department-run clinics, including 24-hour sites in Manhattan and Queens, are continuing to operate, said health commissioner Dr. Dave Chokshi, who joined de Blasio at a video briefing.

An additional three sites run by the city's public hospital system are running, "but vaccine is running low and all of the appointments are filled," said Dr. Mitchell Katz, head of the hospital system.

The hodgepodge of locations where people can get vaccinated in New York City also includes private hospital systems, state-run sites and sites run by unions or employers. Some of those sites have also canceled or postponed appointments. Mount Sinai Hospital announced last week that it would "temporarily pause scheduling of non-employees" from Jan. 15 through Jan. 19.

The cancellations are an unwelcome hurdle for New Yorkers who struggled to book appointments in the first place.

Rosa Schneider jumped on the chance to book a vaccination appointment once she heard that educators like her were becoming eligible in New York. The 32-year-old high school English teacher lives in New York City but works at a New Jersey school where in-person classes are due to resume in late February. 

She said that a day before her vaccine appointment on Wednesday at a city-run hospital, she got a call saying the supply had run out and the appointment was canceled.

"I was concerned, and I was upset," said Schneider, but she is trying daily to book another appointment and hopeful that availability will improve.

Kevin Collymore, a university administrator who also teaches at times, said he was due to get vaccinated this coming Monday at a state hospital in Brooklyn — until he got a voicemail Tuesday saying the appointment was nixed.

Collymore, 32, is taking it in stride: "If it's not meant to be now, I'll just continue to wait," he said. But he's worried for his mother, a home attendant hoping to schedule a vaccination in the coming weeks.

Cancellations and concerns have been stacking up around the state, with Cuomo saying Wednesday he expected it to exhaust its vaccine supply within two or three days for people seeking their first dose.

Mark Buddle, who teaches physical education in-person to high school students in Schenectady, started hunting for appointments as soon as he could and felt lucky to snag one for Feb. 11. But then he got an email Wednesday saying the site was out of vaccine and was canceling appointments, he said.

He managed to rebook — for March 27 in Utica, at least a 90-minute drive away. 

It's good to have something set, but "the uncertainty is very frustrating," Buddle said Thursday. "Because when you lose it, like I did yesterday, you kind of have that despair of 'when will I ever be able to get one?' And to learn that it was March 27 was not reassuring."

In New York City, Joan Jeffri, 76, said she got and lost vaccination dates three times before finally receiving her first shot Wednesday at a hospital that had canceled on her previously.

"Third time's the charm," she said.