Homes could be built on the site of a former psychiatric hospital in the Brecon Beacons under plans by a housing developer.
Collins Developments (Pontrilas) Limited of Herefordshire has bought the former NHS site in Talgarth, near Brecon, Powys.
A local action group claims 100 houses could be built and it is concerned about the scale of the proposals.
The firm said plans were at an early stage and it was aware of the concerns.
Talgarth hospital closed in 1999 and there have been a number of attempts to redevelop the 11-acre site since.
The building and land have been bought by Collins Developments Pontrilas Limited, a subsidiary of Collins Design and Build Limited, which is based near Hereford.
Managing director Phil Collins attended a public meeting in Talgarth recently and questions were put to him about his plans.
The local action group, Mid Wales Hospital Adjacent Adjoining Neighbours Group, claimed there were "tentative plans" for 100 houses and some offices, but Mr Collins said proposals were at such an early stage that he could not provide a figure for the homes.
Talgarth town councillor and group member, Niel Bally, said: "Alarm bells went off when Mr Collins referred to the scheme as a satellite village.
"The site has great potential and we are keen to see it developed but it must be the right development not any development.
"The scale of the housing idea proposed by Mr Collins is of concern as it seems to disregard requirements of the Brecon Beacon National Park Authority.
"Recently the authority has said it would be 'prepared to accept an element of housing and is keen to enable a range of uses on the site, particularly employment generating uses'.
"Now Mr Collins is proposing about 10% of the mixed-use area for offices and the remaining 90% for housing. 90% can hardly be called an 'element' and provisions have to be made for community facilities and affordable housing."
Mr Collins said he was in negotiations with planning consultants and architects to come up with a scheme to redevelop the site.
He added: "These plans are at a very early stage and we are aware of local concerns, particularly following the meeting we contributed to at the town hall a few weeks ago.
"There is not much point in expanding on this because the plans are still extremely fluid and there are so many issues to be dealt with together with further consultation with the community before any formal application is made."
Action group chairman John Dunne said the hospital closed in 1999. Since then there had been a number of attempts to redevelop the site, which he said had all ended in failure.