FRANKLIN, MASS. (WHDH) - Twelve people were taken to the hospital following a carbon monoxide leak inside a gym at the Franklin Village Mall on Thursday morning, authorities said.

Crews responding to the mall at 250 Franklin Village Drive found “very high levels” of carbon monoxide inside 9Round Kickboxing, according to Franklin Fire Chief James McLaughlin.

Most of the carbon monoxide readings were said to be taken on the second level of the building.

“We immediately got fans, opened up doors, ventilated it, and made sure everybody was out of that affected area,” McLaughlin said.

The owner of the gym, Teraisa Sabatini-Tucker, told 7NEWS that a trainer noticed an odd smell around 6 a.m. Tucker then contacted Columbia Gas, prompting a large emergency response.

She says crews found the source of the leak inside a dry cleaning business next door.

Those transported to the hospital were complaining of upset stomachs and nausea, according to McLaughlin. There was no immediate word on their condition.

The gym will remain closed Thursday but will likely reopen on Friday.

This is a developing news story; stay with 7NEWS for updates online and on-air.

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