The Japan External Trade Organization's (JETRO) survey of over 1,000 Japanese businesses operating in Ho Chi Minh City and southern provinces found 60 percent had a 10-50 percent fall in revenues in March.
Over 70 percent of them forecast the severe impact to continue during the second quarter and beyond.
Thirty six percent said their revenues for the year would drop by 20-40 percent while 5 percent said they would fall by over half.
Thirty percent said the pandemic could cost them 10 percent of their revenues.
Sixty one percent wanted the Vietnamese government to provide quick and accurate information about the pandemic and the measures it is taking.
Fifty percent wanted the government to soon restart flights between Vietnam and Japan and relax entry restrictions. The restriction of movement meant many companies had to adjust their personnel plans, including for foreign experts.
Ministry of Labor, Invalids and Social Affairs data shows that 24,410 foreigners have not returned to the country to work.
Japan was Vietnam’s fourth largest investor in terms of registered capital in 2019, after South Korea, Hong Kong and Singapore.
Vietnam's infection tally was 268 as of Friday morning, with 91 people now in hospital and the remaining 177 being discharged after recovering.
Covid-19 has spread to 210 countries and territories, claiming 145,300 lives.