Shoppers were evacuated from Woolworths, Aldi, Chemist Warehouse and Saigon Village Fresh Food Centre on Saturday afternoon after reports of a chemical smell about 12.45pm.

The stores, at the corner of Nicholson and Victoria streets, were emptied by firefighters.

Melbourne Fire Brigade Commander Rick Gili said several people felt unwell as a result of concrete-sealing works at Dimmeys.

"On level one, one of the occupancies polished the concrete and when they applied the gloss finish, it was quite pungent and let off a lot of fumes," he said.

"The fumes permeated the complex and made a lot of people feel quite sick."

He said the fumes were highly flammable and toxic.

Commander Graeme O'Sullivan said the main chemical compound in the floor sealant was called xylene.

"When there's heavy concentrations of that product being used, it [lets off gas] and if there's not adequate ventilation, you can start to get people having respiratory issues, so they start to get irritation in their throat and nose.

"MFB will continue to have a presence there, with Hazmat technicians continually doing air monitoring."

Ambulance Victoria spokesman John Mullen said one man was assessed for breathing difficulties but no one required hospital treatment.

Woolworths remains closed. ???