Two American missionaries who contracted Ebola while treating patients in Liberia have left hospital after making a full recovery, doctors said on Thursday, as authorities in the west African nation struggled to deal with their dead.

Doctors Kent Brantly, 33, and Nancy Writebol, 60, caught the disease in Monrovia in the midst of an outbreak that has killed 1,350 people since March in Guinea, Liberia, Nigeria and Sierra Leone.

The pair were given experimental drugs before being airlifted back to the United States, where they have been treated at a hospital in Atlanta for the last three weeks. 

"The discharge from the hospital of both these patients poses no public health threat," said Bruce Ribner, director of Emory Hospital's Infectious Disease Unit.

The news of their recovery came as west African countries intensified their efforts to contain the worst-ever outbreak of the disease ahead of the arrival of the UN's top Ebola official in the region.

Senegal closed its land borders with Guinea on Thursday, the interior ministry said.

The borders with Guinea, where the virus has killed 396 people, had been sealed earlier this year during an initial stage of the outbreak but Senegal re-opened them in May after the government thought it was under control.

Liberia, which has seen the biggest toll in this epidemic with 576 deaths, has witnessed chaotic scenes in recent days following a surge in cases.

The Red Cross said the crematorium in the capital Monrovia was struggling to deal with the dozens of bodies being brought in each day.

Crematorium workers were having to return corpses to a hospital in the city because they "did not have the capacity to cremate all the bodies", Fayah Tamba, the head of the charity's Liberian office, told a local radio station.

Her comments came a day after troops used tear gas to disperse protesting crowds after President Ellen Johnson Sirleaf ordered a nightime curfew and quarantine zone in Monrovia's West Point slum and Dolo Town, to the east of the capital.

Guinea, where the outbreak first appeared earlier this year, sent more than 100 doctors and volunteers to its borders with Sierra Leone and Liberia to monitor people crossing the border for symptoms.

The death toll from the epidemic now stands at 1,350 after a surge of 106 victims in just two days, most of them in Liberia, according to the World Health Organization (WHO).

The UN's new pointman on Ebola arrived in the region on Thursday for a visit aimed at shoring up health services there, many of which have only recently emerged from many years of devastating conflict.

David Nabarro, a British physician appointed last week by UN Secretary-General Ban Ki-moon, said he would focus on "revitalising the health sectors" in affected countries.

Nabarro was due to visit Monrovia, Freetown, Conakry and Abuja as part of his overall mission to coordinate the global response to the crisis.

Authorities have been hampered in their fight against Ebola by the death of several top health officials and numerous frontline doctors to the virus.

A doctor who treated Nigeria's first Ebola patient was named among the dead on Tuesday, taking the death toll in Africa's most populous country to five.

Other countries have also lost top health professionals.

Fears that the virus could spread to other continents have seen flights to the region cancelled, and authorities around the world have adopted measures to screen travellers arriving from affected nations.

South Africa on Thursday issued a ban on non-citizens travelling from Guinea, Liberia and Sierra Leone, which it labelled "high risk countries".

But despite the rising death toll, WHO spokeswoman Fadela Chaib this week noted "encouraging signs" in Nigeria and Guinea, where prevention measures and work to trace lines of infection were starting to take effect.

The Nigerian outbreak has been traced to a sole foreigner, a Liberian-American who died in late July in Lagos. All subsequent Nigerian victims had direct contact with him.

In Sierra Leone, where 374 people have died, the outbreak has also been traced back to one person: a herbalist in the remote eastern border village of Sokoma.

No cure or vaccine is currently available for Ebola, which is spread by close contact with body fluids, meaning patients must be isolated.

Given the extent of the crisis, the WHO has authorised largely untested treatments -- including ZMapp and the Canadian-made VSV-EBOV vaccine, whose possible side effects on humans are not known.

Three doctors in Liberia who had been given the experimental US-made ZMapp are reportedly responding to the treatment.

Ireland's health service meanwhile said authorities were testing a "suspected case" after a person who travelled to an affected area in Africa was found dead.

The case is in Donegal in northwest Ireland. Test results are expected late on Friday. (AFP)