Hundreds of people living in Co-Op City got a shock today when they learned that their COVID-19 shot appointments were canceled after they arrived at the vaccination site.

The city's Department of Health tells News 12 that 600 appointments had to be canceled at the Co-Op City mass vaccination site.

In a tweet, the DOH said a glitch in the system that sets up the appointments had overbooked people, so there were more appointments than there were doses.

Some people on social media said they got emails about the cancellation, while others showed up and were rescheduled for tomorrow.

The site has been open since March 4. It's a location that elected officials in the area had pushed for.

In spite of Wednesday's issues, when the site opened a month ago the vaccination rate in the community was at 7% -- half the state average at the time. Today, 30% are vaccinated, according to the city -- much closer to the state average.

News 12 is told that all impacted appointments are being rescheduled for Thursday or Friday of this week at the same site. Residents can expect to receive a confirmation email informing them of their new date.