Disaster on election day?

Factual Questions
1

What happens if there’s some kind of disaster on an election day (in the US)? Say the 911 attacks had happened this year in November, so large chunks of the city were closed for the disaster and rescue personnel were tied up managing the disaster, or a hurricane or some other big natural disaster led to similar disruptions. Are there procedures for opening alternate sites, allowing people who were unable to vote for reasons beyond their control to vote later, etc?

I’m aware that election laws in the US vary a lot by locality, but I suspect there’s some general rules of thumb.

2

9/11 was a local election day for New York City. It was the mayoral primary, I think.

They merely cancelled the election and rescheduled it for a later date.