Young people must have access to decent and productive work in order to prevent lasting and irreversible damage, the report added. "The scarring of young people who are excluded from the labor market early in their careers is well attested by the literature".
There are around 267 million young people not in employment, education or training worldwide, the ILO said in a statement.
It says young women have been especially hit by the increase in unemployment.
"They have been basically ejected from their jobs", he said, referring to the one in six youths who have stopped working.
The agency says young people were already in a precarious position relative to other age categories, with work rates still below those before the 2008 economic crisis.
It said that in countries with strong testing and tracing, the average fall in working hours is reduced by as much as 50 percent.
In the United States for example, the jobless rate for young men went from 8.5 per cent in February to 24 per cent in April. Young women are expected to have lost out the most.
In Canada, the overall jobless rate rose six percentage points from February to April, but for young men it swelled by 14.3 percentage points (to 27.1 percent) and for young women it ballooned by 20.4 percentage points to 28.4 percent.
It was "worrisome" that the USA labour market remained "difficult" while other countries easing lockdowns had started to see modest recoveries, said the director of its Employment Policy Department, Sangheon Lee.
The pandemic has slammed young workers with a "triple shock" by killing their jobs, disrupting their education and creating barriers to entering the labor market or moving between gigs, the ILO said.
In its assessment of the pandemic's impact on employment worldwide, the ILO found that the Asia and Pacific region suffered more than twice the amount of lost working hours - a measure used to estimate job losses - versus the global average in the first quarter of 2020.
'If their talent and energy is sidelined by a lack of opportunity or skills it will damage all our futures and make it much more hard to re-build a better, post-COVID economy, ' Ryder warned.
Ryder said he was "extremely concerned" about young people who are being affected disproportionately by the crisis, saying this might lead to a "lockdown generation".
To support youth, the Geneva-based organization called for urgent, large-scale and targeted policy responses, including broad-based employment and training guarantee programs in developed countries, and employment-intensive schemes and guarantees in low- and middle-income economies.
It said that rigorous testing and tracing of COVID-19 infections help minimize labor market disruption, and achieve "substantially smaller social disruptions than confinement and lockdown measures".
In addition, testing and tracing can itself create new jobs, even if temporary, which can be targeted towards youth and other priority groups, ILO said. TT reduces reliance on strict confinement measures; promotes public confidence, and thus encourages consumption and supports employment, and it helps minimise operational disruption at the workplace.