Crews are battling over 100 fires amid a heatwave which has produced the nation's two hottest days on record.
Two volunteer firefighters died in a road accident on Thursday while deployed to a huge blaze near Sydney.
Mr Morrison said he would end his leave early. His absence this week has drawn condemnation and protests.
"I deeply regret any offence caused to any of the many Australians affected by the terrible bushfires by my taking leave with family at this time," he said on Friday.