The incident took place in Sairang, a town around 20 km (12 miles) from the state capital Aizwal, Mizoram Chief Minister Zoramthanga said on messaging platform X, formerly known as Twitter.
Local media reported that around 35-40 workers were at the site when the incident occurred.
"Rescue operations are underway and all possible assistance is being given to those affected," India Prime Minister Narendra Modi said on messaging platform X.
India is not unfamiliar with such bridge mishaps.
In October last year, a colonial-era suspension bridge collapsed in Morbi in the western state of Gujarat, killing 135.
In June a suspension bridge being built in the country's poorest state of Bihar collapsed, killing one person.