Closure of schools during COVID-induced lockdowns across the world had a "deep impact" and spiked the "global mental health crisis" in young children, according to a recent report by the World Health Organisation (WHO).

The report said that globally there was a greater change in the prevalence of major depressive disorders and anxiety disorders, among younger age groups than older ones, potentially reflecting the "deep impact of school closures and social restrictions on youth mental health"

Extended school and university closures interrupted routines and social connections, meaning that young people missed out on learning and experiences expected for healthy development. The disruption and isolation fuelled feelings of anxiety, uncertainty and loneliness, and led to effective and behavioural problems.

"Restrictions imposed during the COVID pandemic for example had significant mental health consequences for many, including stress, anxiety or depression stemming from social isolation, disconnectedness and uncertainty about the future," the report said.

"For some children and adolescents, being made to stay at home is likely to have increased the risk of family stress or abuse, which are known risk factors for mental health problems," it added.

The WHO report estimates more than one billion people are living with a mental health condition, after increasing by more than 25 per cent during the first year of the pandemic. The report also found bullying and sexual abuse were the largest contributors to increased depression in children across the world.

While before the pandemic, the WHO estimated as many as one in seven (14 per cent) of children had a mental health disorder. The rise in the condition post-pandemic in children could be significant.

The WHO has called for urgent action on transforming mental healthcare. The report also urged all countries to accelerate their implementation of the Comprehensive mental health action plan 2013-2030.

It makes several recommendations for action, including stepping up investments in mental health, reducing risks, building resilience and dismantling barriers that stop people with mental health conditions from participating fully in society, and diversifying and scaling up care options for all mental health conditions.