Hundreds of flights have been delayed at Denver International Airport, with authorities noting severe weather and thunderstorms in the region.

Meanwhile, the National Weather Service issued a tornado watch for Denver, Fort Collins and several surrounding counties. As of 5 p.m., a tornado warning had been issued for Adams County.

The weather service also said the threat of very large hail — more than 3 inches — is increasing on Monday afternoon, especially for areas near I-70 from just east of downtown Denver to the Kansas border.

“Take the necessary safety precautions if a warning is issued!” the weather service warned.

Flightaware.com said nearly 700 flights have been delayed as of 5 p.m., though there had been only two flight cancellations. It’s not immediately clear what caused the flight cancellations.

In a status update, the Federal Aviation Authority said a traffic management program has been implemented at DIA for arriving fights due to “weather/thunderstorms.”

Additionally, tornado alarms around Denver inadvertently sounded just after 4 p.m., even though there is no tornado threat in the city, according to the Denver Office of Emergency Management in a social media post.

“The cause of the activation is being reviewed, and appropriate steps will be taken to prevent similar incidents in the future,” officials wrote in the post.