The poll of more than 8,670 teachers, school leaders and support staff found that 83 per cent had seen the issue worsen over the last two years.
The National Education Union (NEU), which carried out the survey, claims increasing child poverty, and an "exam factory culture of over-testing" is behind the rise, as well as insufficient resources for supporting vulnerable pupils.
In response to the survey, one education worker commented: "Sats pressure and general expectations are taking their toll on more vulnerable pupils. We have nine-year-olds talking about suicide."
"Much more anxiety, self-harming," was another comment, which added: "Three suicides in three years in my school alone."
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Another said: "More pupils seem to have anxiety about doing well at school and worry a lot."
The news comes a day after Labour leader Jeremy Corbyn pledged to ban Sats in English primary schools should the party get elected.
Addressing the NEU's conference this week, Corbyn received a standing ovation from members who have been calling for the primary school tests to be scrapped for several years.
Members were also asked if they had appropriate provisions in the workplace for supporting pupils with mental health issues, with 59 per cent reporting they have learning support assistants, and fewer than 50 per cent a school counsellor.
External specialist support was only available to 30 per cent - with a similar rate for school nurses, according to the survey.
One member commented: "I spend most lunchtimes and 40 per cent of my time nurturing children experiencing a range of mental health issues.
"I am currently working with 15 children who have been bereaved, have anxiety, have post-traumatic stress disorder or a parent with a terminal/life threatening illness."
Another commenter reported the local area's wait for a counsellor being more than a year.
"Lost our school counsellor due to lack of funds," said another.
In addition, government-recommended mental health first aiders were only providing support in 12 per cent of schools, according to respondents.
"Mental health first aid is a lip service," said one, who added: "Seven members of staff trained - nothing we didn't already know and it does not make us mental health practitioners."
In multiple-choice responses, 57 per cent of members blamed "real-terms funding cuts", and 51 per cent put the problem down to a reduction in teaching assistants.
Some 53 per cent named an "exam factory" system as a factor, with 64 per cent citing personal workload.
Strain on external support services such as child and adolescent mental health (CAMHS) and specialist SEND assessments, as well as educational psychologists, were highlighted by 64 per cent.
NEU joint general secretary Kevin Courtney, said that it was "very clear" that government policies on education and funding were contributing to a "growing crisis" for mental health that is "damaging the next generation from an early age".
"Teachers are also witnessing an increase in child poverty and its terrible effects, which can all too often impact negatively on mental health," added Courtney.
"Above all this is about pupils, and it is incumbent upon the education system to do all it can to support anyone with mental health problems."
The Department for Education described children's mental health as a "key priority" for the government, and compulsory health education for all children will teach them "how to look after their mental wellbeing and recognise when classmates are struggling".
It added in a statement: "We are investing more in mental health support - with an additional £2.3bn a year being spent by 2023/24.
"This means that by 2023/24 an extra 345,000 children and young people up the age of 25 will benefit from a range of services, including new support teams that will provide additional trained staff to work directly with schools and colleges."