• Russian bombs and missiles have rained down across multiple parts of Ukraine following Vladimir Putin's decision to invade the country of 44 million.
• By Friday evening, Russian reconnaissance troops were within miles of Kyiv's city center, Ukraine's defense ministry said.
• "Strikes on Kyiv with cruise or ballistic missiles continued," it reported.  
• Residents of the capital are sheltering in basements, parking garages and the city's underground metro for safety.

Natasha Suslenko woke up at 4:30 a.m. Friday morning to the sound of air raid sirens and bombs across her hometown of Kyiv, Ukraine's capital, warning of Russian attack. For the second day, she had to grab her things and move into her building's basement parking garage for safety.

"We just put on our clothes in one second, took our child and went down to the parking garage," Suslenko told CNBC from Kyiv. Because of the cold winter weather, family members make sporadic visits back to their apartments to take naps when they deem it safe. Thousands of others sleep in the Kyiv metro, which is now serving as a massive bomb shelter. 

On Thursday, the first day that the sirens rang out across Kyiv as Russian troops invaded the country from multiple flanks, Suslenko made sure to grab all her family's important documents as well. 

"Some people left town," she said. "We decided to stay because we have a small kid, one year old. So it's pretty hard." More than 100,000 people have fled Kyiv so far, heading west or trying to leave the country altogether. Outward road traffic is backed up for miles with "so many, many cars, like zombie movies," she said. 

By Friday evening, Russian reconnaissance troops were within miles of Kyiv's city center, Ukraine's defense ministry said. "Strikes on Kyiv with cruise or ballistic missiles continued," it reported.  

Passenger flights over Ukrainian airspace have been completely halted, and Russian forces have attacked most of the country's airports. Videos showing Ukrainian airbases as well as civilian areas hit by Russian missiles and bombs are being shared widely on social media, though specific reports from the country are difficult to confirm.

Western leaders had warned of a Russian invasion for months as President Vladimir Putin implemented a troop buildup of more than 100,000 of his forces along Ukraine's border. Putin rejected and scoffed at the West's allegations, only to make a fiery case early Thursday morning for a "special military operation" to "demilitarize" the country after denying its statehood. So far at least 200 Ukrainians, both civilian and military, have been killed, while Ukrainian forces push back against Russian troops who have also sustained casualties in the hundreds. 

'I feel helpless'

Nine hundred miles south, in Cyprus, Natasha Suslenko's husband Andrii anxiously checks his phone. He left Ukraine just days before on a work trip and is now stuck, with no way of getting back home. 

"I feel helpless because I'm here and my wife is there, and it's a very emotional, desperate situation," he told CNBC via video call. He's still working in his capacity as a business coach and consultant, helping his Ukrainian clients crisis-manage their businesses. He worries for his parents as well, who are back in Kyiv with his wife. 

"My family was devastated" by Russia's sudden invasion, Suslenko said. "They were 65 and they were not expecting this. My mom was in denial for all the months before, like, 'no, it's not going to happen'. It was unbelievable."

The news stunned the world, and followed protracted NATO-Russia negotiations over security demands — like Putin's demand to prevent Ukraine from ever joining the 30-member alliance and to make the group revert to its 1997 parameters — that NATO leaders deemed to be unacceptable. 

Some analysts say that Putin made these demands knowing the West couldn't accept them, in order to justify an invasion after his government's recognition of two Russian-backed breakaway territories in eastern Ukraine, the People's Republics of Donetsk and Luhansk. Putin has long held that Ukraine — a democracy independent for 30 years — belonged to Russia and that the dissolution of the Soviet Union was the "greatest catastrophe" in history. He also vocally opposes its westward turn toward the EU and NATO.

'We are holding on'

In Ukraine's eastern city of Mariupol, a mere 30 miles from the Russian border, Olga Pereverzeva sits in her entrance hallway, the safest place in her home because it has no windows. "I will probably sleep here, because it's dangerous to be near windows," she said. 

"There's nowhere to run. All of Ukraine is under attack."

She has heard bombing for the last two days, and says many people have fled the city, but that most are remaining so far. As of Friday evening she still had water, electricity and gas, as do the residents of Kyiv that spoke to CNBC.

"We are holding on. We don't lose hope. We believe in our army," she told CNBC. "They are heroes." 

Ukrainian armed forces have repelled several Russian attempts to take territory and some airports, and have shot down numerous Russian helicopters and fighter jets despite being significantly outgunned, Ukraine's Defense Ministry reported Friday. 

"But," Pereverzeva said, "we would be grateful for more help from the world." 

Liza Borysova, a Kyiv native, has an agreement with her best friend to call one another to make sure they are awake in the event of an air attack warning, which often comes through official and unofficial Telegram channels. 

"People are literally afraid to sleep, because then they might not get to the bunkers or pack their things quickly enough," when the bomb warnings go off, she said. 

On its own against Russia

NATO leaders have made it clear that they will not send their troops to help Ukraine, since it is not a member of the treaty organization. That means that aside from weapons and funding, Ukraine is on its own. 

The U.S. and Europe have announced new sanctions on Russia, but Ukrainians and analysts alike say they aren't as harsh as they could be and will not stop Putin. Russian markets rallied on Friday, a sign of local relief that the Western punishments so far were not as bad as feared.

"We're losing trust in our Western partners," Andrii Suslenko said, saying that he wants to see more weapons and funding to Ukraine and sanctions that sever Russia from the global SWIFT payments system. "We'd like to see more action, and this is really lacking. The resources that we have are limited." 

Civilians are taking up arms on the encouragement of the government to form "territorial defense units." The same day Ukrainian President Volodymyr Zelenskyy announced that anyone who wanted to defend the state would be given a firearm, more than 10,000 people signed up for the defense units, Suslenko said. 

"They're ready to defend the city, it is amazing to see," he said. 

"This is what the Ukrainian nation is about, they're volunteering, they are supporting," he said. "And we've seen it many times in the last 30 years."

Ukraine's government announced Thursday that men between the ages of 18 and 60 are no longer allowed to leave the country and must stay and fight. Emotional footage of tearful husbands, wives and parents parting due to the new conscription law have flooded social media. 

Military analysts have expressed surprise at the tenacity of Ukraine's forces in repelling Russian advances so far. But far worse could yet come, raising the specter of higher casualties and prolonged fighting. Still, Ukrainians have vowed not to give up.

"The Russians are attacking Kyiv from four sides, still our army fights back," Natasha Suslenko said. "We are united in our will to live in our country the way we want."