President Ernest Bai Koroma urged people to heed the emergency measures as health workers, some clad in protective biohazard suits, went house to house, checking on residents and marking each doorway they visited with chalk.
Radio stations played Ebola awareness jingles on repeat and encouraged residents to stay indoors.
"As they are fighting this Ebola, we pray that it will be eradicated. That's what we are praying for," said resident Mariam Bangura as she waited at her home in Freetown's West End neighborhood. Other residents looked out over the normally bustling seaside city from windows and balconies.
Nearly 30,000 health workers, volunteers and teachers aim to visit every household in the country of six million people by Sunday to educate them about the disease and isolate the sick.
In Freetown, teams got off to a slow start, waiting several hours to receive kits containing soap, stickers and flyers.
A few police cars and ambulances, sirens blaring, were the only traffic on the otherwise empty streets. One emergency vehicle was seen stopping at a house to take on a patient.
Ebola has infected at least 5,357 people in West Africa this year, mainly in Sierra Leone, Guinea and Liberia, killing 2,630 of those, according to the World Health Organization. The disease has also been reported in Nigeria and Senegal.
The outbreak of the hemorrhagic fever is the worst since it was identified in 1976 in the forests of central Africa.
Western nations, led by the United States, have pledged in recent days to ramp up their aid effort and the United Nations said on Thursday it would deploy a special mission, calling the outbreak a "threat to international peace and security".
"As the disease spreads, a truth becomes clear. None of us is insulated from the threat of Ebola. All of us must be part of the response," Secretary-General Ban Ki-moon told the U.N. General Assembly on Friday.
In Sierra Leone, at least 562 people have died so far from the disease.
"Today, the life of everyone is at stake, but we will get over this difficulty if we all do what we have been asked to do," President Koroma said in a television address late on Thursday.
"These are extraordinary times and extraordinary times require extraordinary measures."
Some have questioned whether the campaign will be effective. Sierra Leone newspaper Awareness Times in an editorial called the preparations for the lockdown "chaotic" and recommended its postponement.
"This morning many families are calling on the radio crying because of lack of food in their homes," said Ahmed Nanoh, executive secretary of Sierra Leone's chamber of agriculture.
"Food prices have gone up 30 percent. Many homes that cannot afford (food) are starving".
Medical charity Medecins Sans Frontieres, which has been at the forefront of the effort to contain the epidemic, warned last week that the lock-down could lead to the concealment of cases, potentially causing the disease to spread further.
An official for the United Nations children's agency UNICEF, Roeland Monasch, said, however, that the "Ose to Ose" campaign, which means "house to house" in local Krio, would be helpful.
"If people don't have access to the right information, we need to bring life-saving messages to them, where they live, at their doorsteps," he said.
Investors are worried about the consequences of the lockdown on Sierra Leone's iron ore production. In a bid to reassure them, African Minerals Ltd. (AMIq.L) said it expected no material impact on its iron ore operations.
Guinea pursues killers
Healthcare workers seeking to contain the Ebola outbreak have often been met with deep mistrust, hampering their efforts to stop its spread. One team of eight educating people on Ebola risks in a remote part of southeastern Guinea were killed and their bodies dumped in a village latrine, officials said on Thursday.
While recognizing that the risks faced by health workers, the World Health Organization said that the tragedy must not be allowed to derail the education effort.
"We should continue the dialogue with the community, we should continue to explain our work, continue to show our empathy with the victims, with the families, with the communities," WHO expert Pierre Formenty said.
NGOs warned in a joint statement that the Ebola crisis could set back by a decade economic progress in Liberia, Guinea and Sierra Leone, and called on more governments to follow U.S. steps to expand efforts to stop the disease's spread.
U.S. President Barack Obama said earlier this week it would deploy 3,000 military engineers and medical personnel and other troops in the region. There are currently around 20 military personnel on the ground in Liberia conducting planning and assessment for the mission.
Over the weekend, 45 more U.S. soldiers are scheduled to arrive in Liberia's capital Monrovia to begin setting up a command center, Department of Defence spokesman Rear Admiral John Kirby said on Friday.
In a rare piece of good news, Senegal's health minister said on Friday there was no further risk of Ebola spreading in his country, following the end of a quarantine period for those who came into contact with an infected man from Guinea. State television said the 21-year-old Guinean student was being repatriated on a military aircraft.
Ebola is endemic in forest mammals in parts of Central Africa but the deadly Zaire strain has never previously appeared in West Africa. Scientists say that a fruit bat butchered as bushmeat in Guinea last December probably started the epidemic.
A parallel outbreak has so far killed 40 people out of 71 cases in the Democratic Republic of Congo.