Russian forces entered Ukraine's capital of Kyiv on Friday morning with battles raging in the north of the city, while the government called on residents to "fight the occupation".
Air raid sirens continued to wail over the city of 3 million people, where some were sheltering in underground metro stations, a day after Russian President Vladimir Putin launched an invasion that has shocked the world.
"People were running for cover amid sounds of explosions and machine gun fire," AFP reported.
The loudest explosion was heard in the center of town as pictures began emerging of Russian military vehicles on city roads.
Associated Press reported gunfire in the city center near the government quarter.
Ukraine's defense ministry called on residents to resist the Russian forces. "We call on all residents to inform us of Russian troop movements, prepare fire bombs and stop the enemy," a ministry statement said.
Officials said two Ukrainian military vehicles were captured by invading forces who then headed to the center of Kyiv disguised as local military, foreign media reported.
The recent fighting came as Russian forces attacked numerous targets around the country.
A senior government source in Kyiv said Friday may end up being the most serious day of fighting.
Ukraine's chiefs of staff, meanwhile, said Russia was using the Gomel airfield in Belarus to line up troops to assault Kyiv due to damage to the Hostomel military airport near the Ukrainian capital.
"In order to intimidate the population of Ukraine, the enemy is increasingly choosing to destroy civilian infrastructure and housing," the General Staff of the Armed Forces of Ukraine said in a Facebook statement.
It said Russian troops were advancing on Kyiv from several directions as Ukrainian forces battled around Mariupol in the south and Kharkiv in the north-east of the country.
Kyiv has been under repeated missile fire from the early hours on Friday as residents were urged to take cover underground.
"Horrific Russian rocket strikes on Kyiv," Foreign Minister Dmytro Kuleba wrote on Twitter. "Last time our capital experienced anything like this was in 1941 when it was attacked by Nazi Germany.
Anton Herashchenko, an adviser to the interior minister said that Ukrainian forces downed an enemy aircraft over Kyiv in the early hours of the morning.
The aircraft crashed into a residential building and set it on fire, injuring at least eight. It was unclear whether the aircraft was manned or whether it could be a missile.
A series of explosions were heard in Kyiv earlier, which Herashchenko said were the sounds of air defenses firing at the aircraft. Further explosions could be heard just before dawn, a witness said.
Authorities also said intense fighting was under way on Friday morning in the city of Sumy in the country's northeast, while a border post in the southeastern Zaporizhzhya region had been hit by missiles, causing deaths and injuries among border guards.
Ukrainian President Volodymyr Zelenskiy said that he was named by Russia as their number one target adding that continued Russian aggression against his country showed that sanctions imposed on Moscow by the West were not enough.
Zelenskiy said the world was continuing to observe what was going on in Ukraine.
Addressing the Russian population in Russian at the end of a televised speech, Zelenskiy said the bombing of Kyiv was reminiscent of Nazi Germany's attacks during World War Two.