A man and a woman suffered extensive burns after their tent was set alight in a suspected arson attack.
The 42-year-old woman and 32-year-old man were also assaulted as they got out of the tent, South Yorkshire Police said.
The incident happened at about 01:20 BST on Tuesday on land near to College Road, Doncaster.
A force representative said the man and woman were being treated in hospital for their injuries.
A 21-year-old man suffered minor burns to his hands after his tent was also set alight.
Det Insp Mark Monteiro said: "It is believed that a male or males have entered the area and doused the tents with what we believe to be some kind of inflammable material before setting fire to the tents.
"It is an unbelievable attack and something I'm amazed has happened."
