However, a lack of beds and resistance in affected communities means its advance continues elsewhere, the World Health Organisation (WHO) said.
Underscoring drastic measures being taken to halt the worst outbreak on record of the deadly virus, Sierra Leone put three more districts -- home to over a million people and major mining operations -- under indefinite quarantine.
An outbreak that began in a remote corner of Guinea has taken hold of much of neighbouring Liberia and Sierra Leone, killing nearly 3,000 people in just over six months. Senegal and Nigeria have recorded cases but, for now, contained them.
(READ MORE: Killings in Guinea show mistrust in Africa Ebola fight: WHO )
World leaders and international organisations have warned of a crisis threatening the stability and economies of a string of fragile West African states. But they have also been criticised for doing too little too late.
"The upward epidemic trend continues in Sierra Leone and most probably also in Liberia," the WHO said in its latest update on the disease, which has killed about half of those confirmed and suspected to have been infected.
"However, the situation in Guinea, although still of grave concern, appears to have stabilized: between 75 and 100 new confirmed cases have been reported in each of the past five weeks," it added.
Experts are trying to straighten out data from the ground, where already weak local health systems over been overrun by one of the world's deadliest diseases, muddying information on the current situation.
But most warn that the number of cases recorded so far represents a fraction of the real total, with many victims unable find places to get treated or unwilling to come forward due to fears over the disease.
WHO said earlier this week that the total number of infections could reach 20,000 by November, months earlier than the previous forecast. U.S. Centers for Disease Control and Prevention (CDC) warned between 550,000 and 1.4 million people might be infected in the region by January if nothing was done.
(READ MORE: IMF says Ebola hits economic growth in W. Africa)
DIFFICULTIES OF ISOLATION
Overnight, Sierra Leone's President Ernest Bai Koroma announced that the districts of Port Loko and Bombali in the north and Moyamba in the south would be quarantined.
The step means five of the country's 14 districts are now isolated. The districts of Kailahum and Kenema, in the northeast close to Guinea and Liberia, were already quarantined.
"The isolation of districts and chiefdoms will definitely pose great difficulties for our people in those districts," Koroma said. "(But) the life of everyone and the survival of our country take precedence over these difficulties."
The extension of the quarantine follows a nationwide lockdown at the weekend that Koroma said had been a success but exposed "areas of greater challenges", including the need to rapidly build more treatment centres.
Under the new measures, people will be able to travel through quarantined districts during daylight hours so long as they do not stop. The World Food Programme is meant to provide food to residents living there.
The Ebola outbreak comes a decade into Sierra Leone and Liberia's recovery from intertwined civil wars that killed hundreds of thousands of people in the 1990s.
In this time, both nations have secured billions of dollars in investment, especially from mining firms looking to tap into their vast iron ore reserves.
However, firms operating in the region have appealed to world leaders to do more to fight the outbreak, which they said threatened the region's stability. Border closures and travel bans have hamstrung trade as well as the aid response.
Sierra Leone's new restrictions are likely to hit mining firms. Port Loko is home to London Mining's concession and African Minerals has its rail and port services there.
Axel Addy, Liberia's minister for commerce and industry, said his nation had secured imports of basic food staples until December, but the blow to its mining sector may trigger a recession next year.
Having spread slowly at first, a spike in Ebola cases and warnings of exponential spread in recent weeks spooked international leaders into greater pledges of action. The response is slowly picking up momentum.
Governments and organisations from across the world, including the United States, Great Britain, France, China and Cuba, have pledged military and civilian personnel alongside cash and medical supplies. But aid workers say it is still not enough.
The WHO said Liberia had 315 bed spaces for Ebola patients and aid agencies have promised to set up 440 more, but the country needs a further 1,550 beds that nobody has yet offered to provide. In Sierra Leone, 297 planned new beds would almost double existing capacity, but a further 532 were needed.
The lack of beds means those infected with Ebola are still being turned away from hospitals and must be cared for at home, where they risk infecting yet more people.
As a result, part of the aid response is now focusing on setting up care centres in communities and training locals, including 11,000 teachers in Liberia, to educate people about how to combat the disease.
The first 9,000 of a planned 50,000 kits -- containing protective gowns, gloves and masks for family members to look after Ebola sufferers -- arrived in Liberia, according to UNICEF.
However, WHO said these efforts were still being resisted in neglected, remote communities with a distrust of outsiders, like the one where eight members of an Ebola team were killed in an attack in southeast Guinea last week.
"There are reports from Fassankoni, Guinea, that communities have set up roadblocks to screen entering response teams."