When Russia invaded Ukraine last week, Max Karmazin said he and his friends fled Kyiv to the relative safety of the west of the country.

The Ukrainian has since changed his mind, and, after spending Sunday night with thousands of others in the city's metro system, where they have been sheltering from possible missile strikes, he plans to volunteer to fight in the war.

Russian forces far outnumber Ukraine's, but they have met with fierce resistance particularly in and around cities. Civilians have joined up with local defence forces to support troops in their attempt to repel Russia's advance.

"I tried to escape Kyiv with my friends a few days ago - we left for Berdychiv - that was our first point where we wanted to stay - and then probably move closer to Poland," he told Reuters in the capital.

"But I felt like I should stay, so I left my friends and returned to Kyiv. We spent the night in the metro station underground, and today we are trying to find these guys - local defence units - and we want to join."

Karmazin is one of thousands of Ukrainians across the country who have heeded their president's call to take up arms and fight the Russians.

Russia calls its actions in Ukraine a "special operation" that it says is not designed to occupy territory but to destroy its southern neighbour's military capabilities and capture what it regards as dangerous nationalists.

Men and women have joined territorial defence units in Ukraine and formed their own local militias. Men below the age of 60 have been stopped from leaving the country as hundreds of thousands seek to flee the fighting.

Karmazin said he was not afraid.

"I believe the world is on our side, and you know, we were attacked, it's not our aggression. So I believe we did nothing wrong and we only defend ourselves."

Kyiv resident Alexi agreed.

"There is no need to raise any kind of panic, no need to start a hysteria," he said. "People unite. Yesterday we were building barricades, blocking roads to limit the movement of enemy troops if anything happens."

(Writing by Mike Collett-White)