An Otago dairy farmer said this week's flooding was the worst in years, and he expected his farm to take weeks to dry out.
Heavy rain which hit Otago yesterday returned to the region this afternoon.
MetService has a heavy rain watch in place for areas including Oamaru, Dunedin and Balclutha for 12 hours from 2pm.
Emergency services rescued two people from the roof of their car earlier today, after they were trapped by floodwaters.
The two people in the vehicle that got stuck this morning were trying to cross a flooded road between Balclutha and Clydevale.
Senior Sergeant Jared Kirk of Otago Coastal Police said the driver and passenger were rescued from the car roof uninjured at about 10am.
The incident has sparked a police appeal for drivers to obey road signs.
"We ask that drivers remain patient, keep your speeds down on these roads, and obey all road closure signs," Mr Kirk said.
"Drivers who ignore road warnings are potentially placing themselves and others at risk.
"Drivers also need to be aware that vehicles may not be covered by insurance if they are driven on a closed road."
State Highway 8, from Milton through to Raes Junction and SH90, is now open but extreme care is needed due to multiple slips and flooding.
Forecaster Claire Flynn said further flooding and slips could be possible on already sodden land and roads.
However, rain is not expected to be as heavy as yesterday.
Clutha District Council said Lawrence, Milton and coastal areas could be affected.
SH 90 at Pomahaka River Bridge, South of Glenkenich, is closed due to flooding
State Highway 90 was closed but has now reopened.
Authorities are monitoring the Clutha River, which has peaked at its highest level in about two decades.
Residents along the Clutha River are remaining on alert even as the water recedes.
More rain is forecast and water is being released from the Roxburgh Dam further back along the catchment.
Resident Steve Sellwood told Checkpoint he would spend tonight at a neighbour's house, after spending a sleepless night monitoring the river, which was separated from his front yard by a floodbank.
After days of rain the Taieri and Waipori rivers have spilt onto nearby farmland, inundating paddocks.
Gavin Russell, who has a farm of about 200 hectares in Taieri, said about 60-70 percent was currently underwater.
He said after several floods they were starting to get used to them, but this was one of the worst to manage, because the land was already saturated from earlier rain.
Mr Russell said it may take two to three weeks for the water to drain completely.
The Central Otago town of Lawrence was hit by flooding for the second time in two years this week.
Residents in Lawrence turned out in full force last night to assist emergency services with sandbagging.
However, Chief Fire Officer Rory Tisdall said the town had come out the other side okay.
After flooding last July, local authorities undertook remedial work, which had helped alleviate flooding this year, Mr Tisdall said.
Metservice meteorologist Georgina Griffiths said northern parts of the North Island had also been hit with wild weather, including thunderstorms, hail and waterspouts.
Updates on road conditions can be found on the NZTA site http://www.journeys.nzta.govt.nz/traffic.