Residents of Sierra Leone's capital held a candlelit vigil and celebrations to mark the end of an Ebola epidemic that has killed almost 4,000 people including more than 220 health workers since it began last year.

Following 42 days with no new cases, the West African nation's epidemic was declared over on Saturday at a ceremony attended by President Ernest Bai Koroma and U.N. World Health Organization (WHO) representative Anders Nordstrom.

Thousands of people gathered overnight around the Cotton Tree, a massive tree in the centre of Freetown, for a candlelit vigil organised by women's groups to pay tribute to health workers who lost their lives.

"They died so we could live," university student Fatmata said with tears in her eyes. Many of the health workers who died were infected due to inadequate protective equipment and training.

The country's first confirmed Ebola survivor, Victoria Yillia, told the crowd she was "happy that this disease which almost killed me has finally ended". She appealed to authorities not to forget survivors, many of whom have faced social stigma and persistent health problems.

Elsewhere in the city, residents celebrated the end of the epidemic, which forced schools to close, overwhelmed healthcare systems and hurt the local economy.

"We're happy. I feel free again after a period of bondage in the hands of Ebola," said trader Joseph Katta as he clutched a pint of beer at a pub in the suburb of Lumley.

Ebola has killed more than 11,300 people in Sierra Leone, Liberia and Guinea since the epidemic was announced in March 2014 and about 28,500 were infected, according to WHO data. Sierra Leone's death toll was 3,955 people.

Liberia was declared free of Ebola on Sept. 3, while a handful of cases remain in Guinea.

The 42-day countdown to be declared Ebola-free starts when the last patient tests negative a second time, normally after a 48-hour gap following their first negative test.

The country now enters a 90-day period of surveillance with support from the WHO, which said the monitoring phase was critical to ensure early detection of any possible new cases.

"We now have a unique opportunity to support Sierra Leone to build a strong and resilient public health system ready to detect and respond to the next outbreak of disease or any other public health threat," Nordstrom said at the ceremony.

Fear of the virus transformed the three countries and hampered efforts in Sierra Leone and Liberia to recover from civil wars.

At the height of the epidemic, authorities in Sierra Leone and Liberia ordered people to stay indoors for days at a time in an attempt to identify new cases and slow the disease's spread.