TOKYO (Reuters) -KKR is the leading candidate to buy the Yokohama headquarters of automaker Nissan Motor ( NSANF ) and has offered around 90 billion yen ($609.80 million), a source familiar with the matter said on Thursday.

KJR Management, a real estate unit owned by KKR, submitted the highest bid but negotiations are ongoing, said the person, who declined to be named because the matter is not public.

A 10-year lease-back of the building is a condition of the sale, the source said.

KKR and Nissan ( NSANF ) declined to comment.

Details of the bidding were first reported by Bloomberg.

($1 = 147.5900 yen)