"Some of the victims have already been taken by their families and buried, so we expect around 100 to be laid to rest in the mass burial," he said, adding that most families had agreed to the offer.
The death toll has crept towards 200 after Tuesday's tsunami wiped out a number coastal settlements.
Officials warned that the death toll after the 8.0-magnitude undersea quake would rise further.
"I think we have to assume the missing are probably dead"
Rosemarie North, Samoa Red Cross
Heart-wrenching accounts were emerging after the disaster. Nine people were killed in a single family as dead children were found under rubble and in treetops, underlining the extent of the catastrophe in the remote South Seas islands.
At least seven foreigners were among the dead in Samoa, a popular tropical destination. At least four Australians, a New Zealander and two South Koreans were confirmed dead.
Thousands were left homeless and hundreds injured when the tsunami flattened tourist resorts and fishing hamlets.
"Volunteers are still finding bodies and as time goes on the chances of finding people alive are slimmer and slimmer," Rosemarie North, from the Samoa Red Cross, said.
"I think we have to assume the missing are probably dead."
Aid workers assisted by military were bringing fresh water, food and material for survivors who have been housed in makeshift camps as fears of an outbreak of disease in the tropical heat grew.