An early assessment by farming observers on the impact of the storm indicates an immediate loss in income to the region of more than $20 million.
Mr English, who is also the Member of Parliament for Clutha-Southland, which includes the area that has endured seven consecutive days of storm, visited the region yesterday and said the economic impact from the loss of livestock would be felt nationally.
"It will certainly have a significant local impact, but it is likely to be large enough to impact on GDP, but we are yet to see that."
He expected those details to be known within the next two months.
This will be a second hit on the economy from a natural disaster, with the Canterbury earthquake expected to shave 0.3% off third quarter GDP.
Lamb losses were high, Mr English said, which would have a significant impact on meat companies and businesses that serviced sheep farmers.
Beef and Lamb New Zealand economic service director Rob Davison said this was the peak lambing week for Southland, with 1 million of an expected 4.9 million lambs expected to be born.
While there was wide variation in the storm's impact, if a third of lambs born in Southland this week were to die, as has been reported by some farmers, that would equate to a loss in income of $29 million for the region, or 8% of expected lamb income.
Mr Davison stressed that some farms were hit much harder than others and the exact number of lambs to perish was not yet known.
Some dairy farms have reported milk flows this week 25% lower than normal, which could result in a loss of income for the region of $2.5 million.
Mr English said in an interview the loss of income was farmers' greatest concern, prompting his call for financiers to declare their position on the disaster.
"Banks have done a good job with the Canterbury earthquake by indicating early that they will be flexible in the way they do business. I hope they will do the same here."
After the Canterbury earthquake, banks offered access to emergency funds, personal interest-free overdrafts and loans for up to 90 days, and fees were waived for loan applications, late credit card payments and the early withdrawal of deposits.
They also provided rapid loan approvals and repayment holidays.
Mr English said the cold weather could prolong the misery for farmers by stunting pasture growth and adding to the loss of capital stock, breeding ewes and cows.
Revenue Minister Peter Dunne announced yesterday anyone adversely affected by the storm will be granted a reprieve by the Inland Revenue Department, similar to what was offered in Canterbury.
NZPA reported the IRD would use its discretion to ease the immediate tax burden, such as for late income equalisation deposits and early withdrawals.
