Oamaru Volunteer Fire Brigade Senior Station Officer Peter Mason said two trucks were sent out to one commercial property, New World South Hill, and four residential properties to pump water out and to stop further flood damage.
He said blocked drains put a lot of stress on local infrastructure.
Fellow Senior Station Officer Brett ''Cuz'' Delmare said water kept flowing into the back of the New World store and reached part of the shop itself.
He did not believe the flooding caused much damage to stock and no-one at New World could be reached for comment.
SSO Mason said at no point during the flooding was there risk to life; just to property.
''Probably two of them would have sustained extensive damage.''
He said there was a period of about 30 minutes where heavy rain just fell and low areas experienced flooding.
MetService duty meteorologist Claire Flynn said from 6pm to 7pm 16.2mm of rain fell in Oamaru township.
What happened earlier in the day in Oamaru was breaks in the cloud allowed the sun to heat up the ground and the air closest to the ground rose and that created moisture.
The moisture rose high enough that it caused thunder storms bringing Oamaru its downpour. Further up the island, Ashburton experienced the same weather pattern with the addition of hail.
Sergeant Tony Woodbridge, of Oamaru, said there were no road closures in Oamaru but there were reports of water on some roads to the North of Oamaru and in Alma to the south.
A car was also "washed away" after the heavy rain last night inland of Oamaru at Weston.
