Now, many around the world are left wondering how to help Ukrainians amid the onslaught.
Here are some ways to support the effort:
The nonprofit is collecting donations for its emergency response project to provide medical supplies, humanitarian aid, and support volunteers on the ground.
The group is also partnering with other Ukrainian-targeted organizations like Nova Ukraine, United Help Ukraine, Revived Soldiers Ukraine, Sunflower for Peace, and Euromaidan-Warszava, according to its website.
The organization says it will use funds to purchase "tourniquets, bandages, combat gauzes, sterile pads, and satellite phones." It also says it is arranging "warehouses and points of delivery in Poland and Ukraine."
The charity organization GlobalGiving has started a Ukraine Crisis Relief Fund which will provide shelter, food, and water to the 500,000 refugees and counting. The money will also be used for health and psychosocial care, as well as education and economic assistance, according to the organization's website.
"All donations to the Ukraine Crisis Relief Fund will support humanitarian assistance in impacted communities in Ukraine and surrounding regions where Ukrainian refugees have fled," the fund page reads. "GlobalGiving's local partners are bringing relief to terrified and displaced communities, and they need resources to continue their life-saving work."
The International Rescue Committee is collecting financial donations that will go toward supporting resources and aid to displaced families.
The organization specializes in helping refugees around the world who have been forced from their homes. They target communities where people lack vital resources for resettlement and recovery from crises.
They also play a vital role in resettlement efforts in the United States.
Doctors Without Borders, an organization that provides medical care during humanitarian crises, still has workers in Ukraine despite the ongoing conflict.
Donations to Doctors Without Borders will fund these services as well as mass casualty kits, emergency medicine and preparedness training for local hospitals and more.
"(The) teams in Ukraine are deeply worried about the consequences of the conflict for Ukrainian people and communities," the website read. "As hostilities continue, ensuring people's access to health care and medicines will be critical. Our teams are looking into how they can adapt MSF's activities to respond."
The United Nations High Commissioner for Refugees, the refugee agency for the United Nations, is accepting donations to provide health care, legal assistance and on-the-ground supply support to refugees from Ukraine.
"UNHCR has stepped up our operations and capacity in Ukraine and neighbouring countries," the organization's website read. "We remain firmly committed to support all affected populations in Ukraine and countries in the region."
The online rental company Airbnb announced that it will offer free, short-term housing to up to 100,000 refugees fleeing Ukraine via its non-profit initiative Airbnb.org.
The organization urges anyone interested in opening up their homes to refugees to get involved: "We know that Hosts and guests on Airbnb around the world will be eager to stand up and assist this massive effort to help those fleeing Ukraine," a statement from Airbnb.org read.
"(Airbnb.org) will work closely with governments to best support the specific needs in each country, including by providing longer-term stays," the statement continued.
As a humanitarian crisis unfolds in Ukraine, U.N. Relief Chief Martin Griffiths estimated that more than $1 billion will be needed in aid -- including "food, shelter, health care, water, sanitation and protection" -- over the next three months.
MORE: Russia-Ukraine live updates
People in Need is providing humanitarian aid to more than 200,000 people on the ground in Ukraine. The Czech organization will "provide mainly the most basic needs according to the currently developing situation...(like) cash assistance, food aid (and) hygiene items" in its first phase of support, according to its website.
People in Need also pledged to support countries experiencing an influx of Ukrainian refugees.
The International Committee of the Red Cross has had a presence in eastern Ukraine for years to deliver assistance to those affected by the Russian conflict following the annexation of Crimea, according to its website.
The organization is "vowing continued support for the at-risk families in the region" amid growing concerns over displacement, mass casualty and destruction.
The American Red Cross, in particular, is "sending 30 trained staff to Europe to support emergency communication needs of U.S. military members."
Sofika Zielyk, a member of the Ukrainian National Women's League of America, said the organization is in "full crisis mode" to respond to the invasion.
"This is a war that everybody has to look at and try to help," she told ABC News.
MORE: Why is Russia invading Ukraine? Countries share complex history
Donations so far have benefited hospitals in the eastern Ukrainian cities of Kharkiv and Luhansk, the organization posted on its Facebook page.
UNICEF is working to assist children and families in Ukraine by making sure their critical needs are met, like access to safe water, health care, education and protection, according to its website.
The organization already has 10 child protection case management mobile teams stationed in the country's east to provide "psychosocial care to children traumatized by the chronic insecurity" of the conflict with Russia.
United Help Ukraine (UHU) is working to provide individual first aid kits (containing blood-stopping bandages and tourniquets) and other emergency medical supplies to the front lines.
In addition, UHU is also cooperating with other emergency response organizations to prepare humanitarian aid for civilians that might be directly affected if Russian forces attack.
The Associated Press contributed to this report.