Liberia's armed forces have been given orders to shoot people on sight who are attempting to illegally cross the border from Ebola-stricken Sierra Leone, according to local media reports.

The order was given to soldiers stationed in Bomi and Grand Cape Mount counties on the border with Sierra Leone in hope of preventing the spread of the deadly virus, deputy chief of staff, Colonel Eric Dennis said.

The decision comes as the search for 17 Liberian Ebola patients, who escaped an attack on a quarantine centre in the Liberian capital, Monrovia, continues.

"We have not yet found them," said Liberian Information Minister Lewis Brown.

"Those who looted the place took away mattresses and bedding that were soaked with fluids from the patients."

Yesterday, the World Health Organisation (WHO) urged all countries affected by Ebola to conduct "exit screening" of individuals at all international airports, seaports and major land crossings.

"Affected countries are requested to conduct exit screening of all persons at international airports, seaports and major land crossings, for unexplained febrile illness consistent with potential Ebola infection," a WHO statement on travel and transport in relation to the deadly virus said.

The countries currently affected by the disease, besides Liberia and Sierra Leone, are Guinea and Nigeria.

Liberia has the highest death toll from the disease with approximately 400 citizens killed. So far, more than 1,200 people have died from the disease, which has been described as the worst ever outbreak of the virus.

The symptoms of the highly contagious virus include fever, sore throat, diarrhoea and internal and external bleeding, with a 90% fatality rate.