The flood and storm department said they needed an extra 5,500 tonnes as provisions have been wiped out.
Vo Thanh, a disaster official, said: "The last two floods already caused a lot of hardship, now another one is coming".
About 300 ancient houses in the town of Hoi An, a Unesco World Heritage site, were flooded with nearly one metre of water. Telephones lines have also been cut in many communities.
As well as property destruction, crop damage has cost the area $300m and delayed the coffee harvest.
Since October, the region which includes the Central Highlands coffee belt, has been hit hard by storms and floods and killed nearly 200 people in total.
The three-month storm season, packed with up to 10 typhoons, often ends in Vietnam in October. This year tropical storms have hit later than usual.