The UN body described how taxis filled with entire families, including members suspected of having Ebola, criss-crossed Monrovia "searching for a treatment bed".
"There are none. As WHO staff in Liberia confirm, no free beds for Ebola treatment exist anywhere in the country."
When Ebola patients are turned away from treatment centres, "they have no choice but to return to their communities and homes, where they inevitably infect others, perpetuating constantly higher flare-ups in the number of cases," it said.
Meanwhile Sierra Leone announced plans to visit every home in the country of six million to track down people with Ebola and remove dead bodies.
Ebola, transmitted through bodily fluids, leads to haemorrhagic fever and – in over half of cases – death.
There is no specific treatment and no licensed vaccine.
Researchers reported in Nature Medicine on Monday however that a vaccine tested on monkeys had provided "complete short-term and partial long-term protection" .
The study endorsed testing the vaccine on humans, with first results due by the end of the year.