The Asia Monitor Resource Center, based in Hong Kong, said in all six countries -- Cambodia, China, India, Indonesia, Thailand and the Philippines -- statistics are hard to find, CNN reported. Employers, governments and even doctors are reluctant to look at the problem.
In 2008, the International Labor Organization estimated the number of deaths every year from work-related illness at more than 1 million a year in Asia.
"One-point-one million is a really high number, but even then we're not sure, we think it may be a really conservative number," Sanjiv Pandita, the AMRC's executive director, told CNN.
The group released a report Saturday, International Workers' Day.
"The problem is there is no data, absolutely no data," Pandita said. "You can get quarterly data for economic statistics, but you can't get any data about the workers. … What is their health, how are they faring? There is no data on that."
Wang Fengping, who worked for 15 years as an engineer in a battery factory in China, said cadmium poisoning destroyed her kidneys. She had problems finding a doctor who would certify the illness as work-related, allowing her to apply for compensation.
Pandita said many migrants are not covered by labor laws. In countries such as China, employees may not be able to prove they were working because their employers will refuse to give them copies of their labor contracts.