The decision follows the refusal of some communities to allow the burial of Ebola victims on their land.
Meanwhile, Nigeria says it has a second Ebola case – that of one of the doctors who treated a man who died from Ebola after his arrival from Liberia.
This year’s outbreak, the worst ever, has centred on Guinea, Liberia and Sierra Leone, killing 887 people.
It spreads by contact with infected blood and bodily fluids – and touching the body of someone who has died of Ebola is particularly dangerous.
Nigeria’s Health Minister Onyebuchi Chukwu said that 70 people have been traced who came into contact with the man who died there, Patrick Sawyer, eight of whom are now in isolation.
Sawyer, an employee of the Liberian finance ministry, had arrived in Lagos from Monrovia after changing planes in Togo’s capital, Lome, on 20 July and died five days later in quarantine.
There has been a boom in the sale of tap buckets in Monrovia
There is no cure or vaccine for Ebola – but patients have a better chance of survival if they receive early treatment.
The current outbreak is killing between 50% and 60% of people infected.
Initial flu-like symptoms can lead to external haemorrhaging from areas like eyes and gums, and internal bleeding which can lead to organ failure.
The BBC’s Jonathan Paye-Layleh in the capital, Monrovia, says cremation is not part of the culture in Liberia and health experts say burial ceremonies have played a role in the transmission of the virus.
Liberia’s Information Minister Lewis Brown made the announcement on state radio about cremations after an incident over the weekend when a community refused to allow the burial of some bodies, most of them Ebola victims.