UPDATE 2-S.Africa miners free hostage bosses

(Recasts with release of supervisors)

JOHANNESBURG, July 10 (Reuters) - Some 500 contract workers who were holding seven supervisors hostage at Eastern Platinum's (ELR.TO) (EPSJ.J) mine in South Africa since Thursday released them on Friday evening a company spokeswoman said.

Eastplats said workers at the Crocodile River mine had staged a "sit-in" in an underground area close to the entrance to the mine and have refused to leave the premises. The company said it had removed all other employees from underground.

"The last four of the supervisors held underground during a sit-in at the mine have been released. The sit-in at the mine continues, however," Eastplats spokeswoman Charmaine Russell said in an email. The workers are demanding to be employed permanently, a promise they say they were given by management, a local radio station reported. They were notified early on Thursday that management would not fulfil that promise, it said.

Eastplats said in an earlier statement their demands were in contradiction of agreements in place.

"This demand and associated illegal action is not supported by Eastplats, the National Union of Mineworkers (NUM), or by the mining contractors involved," it said.

Mining contractors are in the process of obtaining a court order which will require their employees to stop the illegal strike action, will enforce the release of those detained and will ask those striking to vacate the underground areas, Easplats said. (Reporting by Agnieszka Flak and Phumza Macanda; Editing by Keiron Henderson)