Plans are being drawn up that could see cuts to NHS services across England.
The BBC has seen draft sustainability and transformation plans (STPs), which propose changes to hospital and GP services.
NHS England says reorganising local services is essential to improve patient care.
But a think tank warned that while STPs could lead to “fundamental changes”, they had not been “visible” enough.
In all, 44 STPs are being drawn up by local health and social care leaders.
They were asked to find potential savings and efficiencies at the end of last year.
Despite being due for sign off in October, many STPs are still unpublished.
They are likely to be implemented in the new year.
The NHS needs to find £22bn in efficiency savings by 2020-21 to meet the financial targets set out by the former Chancellor George Osborne and NHS England head Simon Stevens.
The campaign group 38 Degrees uncovered many unreported draft STPs, including plans for the closure of Midland Metropolitan Hospital’s accident and emergency department, the merging of two of the area’s three district general hospitals and the closure of one site.
In Leicester, Leicestershire and Rutland, there are plans to reduce the number of hospitals in the area from three to two.
There are also plans to put GP surgeries under “review” because of a shortage of funding.
There have been no consultations on the plans so far.
A draft plan circulating among NHS managers in West Yorkshire reveals proposals to close the equivalent of five wards in the Leeds Teaching Hospitals Trust.
A spokeswoman for the area said: “We will be engaging and consulting as and when appropriate.”
In a blog published on the Nuffield Trust website, its head, Nigel Edwards, said STPs had “the potential to make fundamental changes in the shape and nature of health and care services”.
But he added: “The process to shape these plans has meant that they have so far not been very visible.”
Sally Gainsbury, senior policy analyst with the trust, said: “It looks like quite a lot of these plans at the moment are proposing big, large-scale reconfigurations – that’s shifting services or shutting services down.
“Our research finds that, in a lot of these kinds of reconfigurations, you don’t save very much money – all that happens is the patient has to go to the next hospital down the road.
“They’re more inconvenienced, they have to travel further, but it rarely saves the money that’s needed.”
A NHS England spokesman said: “This is a unique exercise in collaboration. It is hardly a secret that the NHS is looking to make major efficiencies and the best way of doing so is for local doctors, hospitals and councils to work together to decide the way forward in consultation with local communities.
“Proposals are at a draft stage but we expect all local leaders to be talking to the public and stakeholders regularly – it is vital that people are able to shape the future of their local services.
“No changes to the services people currently receive will be made without local engagement and, where required, consultation. There are longstanding assurance processes in place to make sure this happens.”
38 Degrees director Laura Townshend said: “This is new evidence that plans are being made to close local NHS services.
“We all rely on these services, yet we are being kept in the dark.
“These proposed cuts aren’t the fault of local NHS leaders.
“The health service is struggling to cope with growing black holes in NHS funding.
“The NHS belongs to all of us – so local people should get a say in any changes to their local services.”
David Pearson, STP leader for Nottinghamshire, told BBC Radio 4’s You and Yours programme: “Sometimes, we have particular conditions or particular treatments that are best in a centre of excellence.
“So, that’s part of the debate we will no doubt have.
“But this is fundamentally about making sure we are doing the best things across Nottinghamshire and that, as far as possible, services are locally delivered to an agreed understanding of what best practice is.
“The transformation of services is rarely just one big dramatic closure.
“It’s thousands of people working with citizens to deliver the best possible outcomes, and that’s what this is about.”