Child protection referrals have plummeted by more than 50% in some areas of England, raising concerns about the welfare of vulnerable children during the coronavirus outbreak.

Local authorities have reported dramatic falls in the number of children being referred to social services over child protection concerns, with social workers in one county in the south-east dealing with 25% of their normal daily level of referrals.

Referrals are usually made by schools and health professionals, so with schools closed and children confined at home during the Covid-19 crisis, they are not coming into contact with the professionals who normally raise protection concerns.

There are also fears for children already known to be vulnerable, as they become less visible. The government had hoped to keep them in emergency schools, making places available for them alongside children of key workers, but attendance so far has been low, with as few as 5% turning up in some places.

School staff and social workers are liaising with parents to encourage them to send their child to school, but they say families are choosing to keep children at home because they are worried about catching the virus. Others do not like the stigma of being seen as “vulnerable”, defined by government as a child with a social worker or an education, health and care plan for those with complex special educational needs.

Children’s services directors contacted by the Guardian said they were concerned about the impact of domestic violence on children during the lockdown. Some reported a small increase in the number of young people reported missing, as teenagers struggle to observe the lockdown restrictions which may prevent them seeing friends and family.

The Children’s Society has also warned that criminals involved in county lines drug trafficking could take advantage of the Covid-19 crisis to target children who are isolated from their usual support networks at school or college.

“There will be a tremendous amount of unseen demand for child protection and for mental health issues,” said Matt Dunkley, the corporate director of children’s services in Kent. “We are currently seeing about 25% of our normal daily level of referrals. If professionals are not seeing these children, those referrals are not being made.”

Looking ahead to the end of the lockdown, Dunkley said: “The biggest challenge will be pent-up demand and how that pans out in whatever the exit from lockdown looks like. I expect demand will go through the roof.”

In Kent, between 10% and 20% of vulnerable children eligible for a school place turned up for school the week before the Easter holidays. In Hertfordshire it was 12%. “After Easter, after families have been together for a considerable amount of time, we are hopeful that the numbers will increase,” said Jenny Coles, the director of children’s services in Hertfordshire. “Schools are a really important part of protecting children.”

In Hertfordshire there has been a 50% decline in the number of referrals over the last week. “It’s really important and we are concerned about it,” said Coles, who is also president of the Association of Directors of Children’s Services.

She said local authorities were prioritising face-to-face contact with those most at risk, but the usual routes of safeguarding referrals were inevitably affected by the lockdown.

“Locally systems are in place to ensure children are protected but now more than ever it’s important that communities and neighbours are looking out for each other where possible, and if a family needs some additional help in these unprecedented times, contact should be made with the local authority as soon as possible so this can be arranged.”

The government was unable to provide official data on school attendance by vulnerable children, but a spokesman said: “Being in school can keep vulnerable children safe and ease pressure on families, which is why we have enabled these children to continue attending despite schools being closed for other pupils.”

As the lockdown continues, pressures on vulnerable families will increase. “At the moment, all things considered, everyone is behaving remarkably well,” said Dunkley. “The longer lockdown goes on into the summer, the greater challenges it will pose to some of our young people.”