July saw a "further deterioration" in manufacturing "as the coronavirus disease 2019 pandemic continued to impact the sector," IHS Markit said.
The survey polled 2,100 factory managers across seven of the 10 member-states of the Association of South-East Asian Nations (ASEAN), a regional bloc.
The survey showed Singapore, the region's wealthiest country, to be affected the worst. A headline figure of below 50 indicates that factories are not running at full steam, and Singapore reported a number of 37.3 compared to a region-wide 46.5.
Myanmar was the only country to record an improvement in July compared to June. Malaysia's manufacturing appears to be flat-lining after a June uptick followed the end of the country's strict lockdown.
Indonesia and the Philippines, the region's two biggest countries measured by population, saw significant retrenchments in manufacturing. Cumulative coronavirus cases in both archipelagos have topped 100,000.
In the Philippines, July "signalled a sharper rate of deterioration than in June amid a renewed drop in output," IHS Markit reported.
In Vietnam, which initially was hit relatively lightly by the pandemic, the figure dropped to 47.6 in July, with the first virus cases in around three months recorded at the end of July.
Most countries across the region face recession this year.
Projected contractions range from 2.8 per cent in Malaysia and to 7 per cent in Singapore, according to both countries' central banks. - dpa