Omeruo joins on loan for the rest of the season.
Karanka told the Evening Gazette: "Kenneth's a defender from Chelsea. I know him, Jose told me about him and told me he's a good player to have.
"We have been working on a deal and he will be with us on Tuesday and staying for the rest of the season.
"He's a strong defender and we need to improve at the back and we need a strong defender. Kenneth is a strong player a very good player, he can play at centre-back and right-back.
"We are looking for many positions, but we need to be very smart with the players that come here because I'm very happy with my squad."