Ninety children are being taken into care every day in England and Wales and it's claimed social workers are "firefighting" the most serious cases late into the night.
Prof Ray Jones, who works in social services improvement, says staff fear children slip through the net as they try to keep up with rising pressures.
Latest government figures show 32,810 children were taken into care in 2017.
Ministers said extra money was being targeted towards improving services.
The total number of children in care is a record 72,670 - up 3% on 2016.
Council bosses, who are responsible for child protection services, say it's the biggest rise in seven years.
The Local Government Association, which is taking part in a conference on care services in Bournemouth, says it comes as children's services face a £2bn a year funding gap by 2020.
Prof Jones said: "What I am hearing from social workers is that they are having to spend most of the time 'firefighting' with the most serious concerns that get presented to them.
"They are spending a lot of time, including late into the night and at weekends, preparing for court proceedings.
"They are also having to close down work very quickly where the child is not an immediate concern.
"The consequence of that is the considerable stress they feel over concerns that they may be missing something."
He added: "Secondly, something that social workers are telling me is that they are closing down cases very quickly or even turning them away.
"And they are not able to work through potential cases where children are unhappy and distressed, because they are having to concentrate on cases where there is an immediate danger."
But the figures continue a longer trend of rising numbers of children facing severe need in terms of child protection.
Richard Watts, chairman of the LGA's children and young people board, said: "Children's services are at a tipping point with growing demand for support combining with ongoing council funding pressures to become unsustainable.
"Last year saw the biggest rise in the number of children in care for seven years.
"With 90 children coming into care every day, our calls for urgent funding to support these children and invest in children and their families are becoming increasingly urgent."
Robert Goodwill, Minister for Children and Families, said councils would receive more than £200bn for local services, including children's social care, up to 2020.
"This is part of a historic four-year settlement, which means councils can plan ahead with certainty.
"All children deserve the best possible support. And while some councils are doing excellent work, we want to help ensure more local authorities provide good and outstanding services."