The new cases were detected from 3,967 samples tested on Tuesday, putting the single-day positivity rate at 7.99 per cent, it said.
Of the fresh cases, Aizawl district reported the highest at 251, followed by Kolasib (21) and Lawngtlai (17), it said. The remaining cases were from Lunglei, Serchhip, Saitual, Siaha, Mamit and Khawzawl districts.
More than 61 children, including a one-month-old baby, were among the newly infected people, the statement said.
Five patients have travel history, while the remaining 312 were found to have locally contracted the infection, it said. The contact history of 99 patients are yet to be ascertained, it said.
Of the 317 patients, 231 have developed symptoms of COVID-19.
Mizoram now has 3,388 active cases, while 10,553 people have recovered from the infection with the discharge of 208 people from various Covid-19 Care Centres on Monday.
The COVID-19 death toll in the state stood at 55.
According to state immunisation officer Dr Lalzawmi, as many as 2,70,606 people have been administered the first dose of COVID-19 vaccine of which 52,376 have received both doses till Monday.