A carbon monoxide leak at a beachfront resort in Ocean City sickened nearly 20 people Friday, sending some to the hospital, forcing mass evacuations and upending vacations.

Four people were hospitalized, 13 were treated on-site and one person refused treatment Friday for carbon monoxide exposure at Ashore Resort & Beach Club, Ocean City Fire Department officials said on social media.

Alarms blared throughout the hotel around 11 a.m. Friday. The incident prompted a large emergency response and triggered a mass casualty designation from officials.

Guests, some just arriving, others already settled in for family reunions or beach getaways, scrambled to evacuate the 250-room hotel. Among them was a woman who had driven eight hours from Charlotte, North Carolina, and was forced to evacuate alongside her 97-year-old grandmother.

Guests did not want to share their full names out of concerns for their privacy.

Another guest who was about to check into the hotel when the front desk told him that there is no hot water, and they don’t expect to have any until Monday. He said hotel staff didn’t say why, nor was he told about the circumstances prior to showing up to check in for his reservation.

Guests have been offered relocation to White Marlin Open between Aug. 4-8. Ocean City’s fire marshal, building inspectors and representatives from the gas company are investigating the cause of carbon monoxide leak.

Ashore Hotel is a beachfront resort with 250 guest rooms located at 10100 Coastal Highway. Before being bought by Certares Real Estate Management, Monomoy Property Ventures and Highlands Investments in 2022, it was known as Ocean City Fontainebleau Resort.

When reached by phone, representatives for Certares declined to comment. Representatives for Monomoy Property Ventures and Highlands Investments did not immediately respond to requests for comment.

The property opened in May 2023 and was ranked as one of the Top 10 Best New Hotels of 2024 by USA Today. The hotel had a lineup of entertainment this month that was slated to begin just before firefighters got the carbon monoxide alarm.

Management at the hotel declined to comment.

This article will be updated.