The number of older people in England needing care will "outstrip" the number of family members able to provide it by 2017, a think tank has warned.
An Institute for Public Policy Research (IPPR) report estimates that by 2030 there will be more than two million people aged 65 and over with no child living nearby to give care if needed.
The IPPR said the country must "build new community institutions" to cope.
The government said it was working to make sure more people got care at home.
The IPPR report estimates that, of the two million people it says will have no child living nearby to care for them in England in 2030, 230,000 will need more than 20 hours of care per week.
'Left to cope'
Clare McNeil, senior research fellow at the centre-left think tank, said the supply of "unpaid care" to older people by their adult children would "not keep pace with future demand".
"Thousands of people in their 60s and 70s today could be left to cope on their own when they need care in the future, with overstretched services unable to make up the shortfall," she said.
"Britain needs to build new community institutions capable of sustaining us through the changes ahead and to adapt the social structures already in place, such as family and care, public services, the workplace and neighbourhoods."
To fill the care "gap", the report suggested the UK should:
widen the use of "neighbourhood networks", highlighting those run in Leeds by older people and offering activities to reduce social isolation as well as providing care and support
invest in strengthening community groups in areas with the "weakest record for community-based care"
follow international examples, highlighting initiatives in Germany, Australia and Japan's 10-year nationwide campaign "to train one million dementia supporters"
house public services for different age groups, such as childcare and care for the elderly, together in the same buildings as is done in Germany
strengthen employment rights for carers
The report also highlights the number of older people providing care, and estimates that the amount of "intensive" care provided by spouses and partners will rise by 90% over the next 15 years.
It says the average annual cost for those who pay for care is currently £25,000 for home care and £36,000 for a nursing home.
The government said it was working to integrate health and council care services to ensure more older people received care at home.
Are you over 65 and without somebody nearby to help you? Or do you have parents over 65 who live too far away to provide care for? You can email your experiences to firstname.lastname@example.org, using the subject line 'Elderly care'.