The A303 in Ilminster is closed following a four-vehicle crash.
A flat bed truck travelling westbound was in a collision with a Vauxhall Corsa travelling in the opposite direction and then two further cars.
The male driver of the truck has been seriously injured.
A man who was in the Corsa also suffered serious injuries.
The road has been closed to enable a full examination of the scene.
This could take several hours and motorists are being urged to avoid the area.
More top news
Britons evacuated from the coronavirus-hit Diamond Princess cruise ship have arrived at Arrowe Park Hospital on the Wirral.
A mild afternoon - cloudy with some sunshine. There will be persistent, heavy rain later.
A cloudy afternoon with patchy rain, but feeling mild. Persistent rain this evening will eventually clear.