Can somebody help identify what has happened to my tomatoes? They went from very healthy looking to this very quickly. Thanks for any help or ideas.

How much are you watering? It really seems like a watering issue.

Also when growing tomatoes in containers or when space is otherwise at a premium it's always better to keep them tidy by eliminating axillary shoots and topping the plant once it reaches a certain height (cultivar dependent). Helps air and sunlight reaching the whole plant thus favoring a better development and it helps keeping diseases at bay as well.

Could be a watering issue. It's easy to drown a plant in a container.

Could also be lack of fertilizer. What are you fertilizing with and how are you applying it. Container plants only have a finite amount of soil to draw nutrients from and need more careful fertilization.

The other thing that comes to mind is maybe early blight.

What is your (rough) location? Gardening is a local thing and knowing where you are located lets people give better gardening advice.

Welcome to the forum!!!
Ed

The plants are packed to tightly in your containers I would say you have an airflow situation and a blight or bacterial disease is taking over. You container is too shallow. One tomato plant in a container of at least 5 gallons is optimum. Then water the bottom, keep the leaves as dry as possible and as mentioned, fertilize every week or ten days with a low nitrogen fertilizer to replace what has been lost in the watering process.

You location will help a lot, what variety(ies) are in the container, temperatures where you are and how much sunshine. More information is always better.

Now what can you do? Open up the bottom a little, remove the dead leaves and throw away. There is some green left and there may be life left in the plants yet.