Chernihiv is located 128km north of Kyiv.
This comes as high numbers of Russian casualties have been reported.
Ukrainian deputy defence minister Hanna Malyar said on Sunday that there may be as many as 4,300 Russian casualties so far.
However, figures have not been officially released by Moscow.
Ukraine has taken an additional 200 prisoners of war, according to an aide to Ukrainian President Volodymyr Zelenskyy.
In an interview with Sky News, UK Defense Secretary Ben Wallace said that 450 Russian military personnel were killed in the first 24 hours of the invasion.
As of Saturday, 198 Ukrainians had been killed in the conflict.
An additional 1,115 Ukrainian citizens have been injured during Russia’s attack, 33 of them children, Ukraine’s health minister Viktor Liashko said.
UPDATES TO FOLLOW…