This is really TheBeardyMan's answer because he pinpointed the novella I was thinking of in a comment above. I'm fairly sure you're thinking of the novella Fiddler's Green by Richard McKenna. The length of the story and the publication date match your description.
This novella appears to be hard to get hold of. I'm fairly sure I read it in the collection Casey Agonistes, and Other Science Fiction and Fantasy Stories but this is long out of print. It's decades since I last read it, but I'll do my best to remember the plot.
The story starts with a group of shipwrecked sailors adrift in a lifeboat and dying of hunger and thirst. They've drawn straws to see who will sacrifice their life to feed the rest, and they're about to kill the loser when one of the group, Kruger, stops them and explains how he thinks they can escape through a portal to another world. The sailors allow themselves to be hypnotised by Kruger, and it works! They find themselves in a dark valley surrounded by mist. When they try to walk out of the valley they somehow find themselves turned around and walking back into the valley again.
As time goes on more people turn up, and it turns out there is a portal sweeping over the Earth's surface. If people are far from civilisation, and an area where the real world is thin, they can get swept up by the portal and transported to the valley. As more people arrive the valley grows and pushes back the mist to get bigger.
But there's a problem. It turns out the Kruger, possibly because of his role in opening the portal did not cross properly. His body appears to be dead, and he exists as a sort of ghost or (as it turns out) minor deity. Also Kruger still suffers the same hunger and thirst that he did in the lifeboat. The story takes a dark turn when Kruger discovers how to quench his thirst.
I was a lot younger and more impressionable when I read the story back in the 70s, but the fact I can remember it forty years later shows how big an impression it made on me. In fact I also loved Mckenna's story "Casey Agonistes" from the same anthology. Sadly Mckenna seems a largely forgotten figure these days.