A police source said poor-quality meat served as shashlik, or skewered meat cubes cooked over coals, could have been to blame for the illnesses. The dish, which is popular across the former Soviet Union, is often served at restaurants but is more commonly sold by street vendors.
"Talking to the workers, [investigators] found out that all of them ate shashlik the day before," a police source said. "This is the only thing all the patients have in common."
He said experts were working to identify the source of the infection, which could take two days.
He also said experts had suggested the workers could have contracted salmonella poisoning, an infection that affects the gastrointestinal system that is potentially lethal.
The emergencies ministry said the first patients had been taken to hospital from a construction site on Tverskaya Street just a few steps away from Red Square and the Kremlin.
The ministry said the workers were from Turkey and former Soviet republics, the main source of cheap workforce for numerous construction projects in booming Moscow, many of which are implemented by Turkish firms.
Poor working and living conditions of migrant workers, particularly from post-Soviet Central Asia who often stay in Russia illegally, have been continuously criticized by the Asian governments and rights groups.