The state of emergency has been extended in the Nelson-Tasman region after a week devastated by heavy rain, flooding and major slips.

The Nelson-Tasman emergency management group said this will enable the emergency efforts to continue being well resourced with support from the central government and all agencies.

It has been extended till 2.54pm on Wednesday August 31, a further seven days from the original declaration.

Devenish Place in Nelson where a culvert turned into a torrent of mud as heavy rains hit. Photo / Supplied

Nelson Mayor Rachel Reese signed the declaration to extend the state of emergency this afternoon and said this recognised the gravity of the effect of the rain event on the region and the critical needs that remained in the community.

"Extending the state of local emergency for another week ensures we have the resources we need to continue supporting our community through the response," Reese said.

"Planning and initial steps for the transition from response to recovery are well underway. The main focus is helping our affected community return to their homes, or to find suitable alternative accommodation as quickly as possible."

Earlier this afternoon, Prime Minister Jacinda Ardern said she and Emergency Response Minister Kieran McAnulty had agreed with Cabinet to open a Mayoral Relief Fund with an initial injection of $100,000.

It was also boosting another package of funding by an additional $100,000 - taking the full amount to $300,000 so far. Ardern said the Mayoral Relief Fund was highly discretionary and aimed at getting money quickly to areas where it was most needed.

Prime Minister Jacinda Ardern walks over the Matai River with Response Controller Alec Louverdis during her tour of flood-hit Nelson. Photo / Tim Cuff

About 570 homes have been impacted by the major weather event, and 350 major slips have occurred since the deluge began.

Ardern said the stories she'd heard were devastating and there was potential for further slips, particularly with more heavy rain on the way.

"You see the scale of the damage and what it's done to people's homes and it is devastating. You can't imagine coming back after being evacuated in a hurry fearing probably for your own family's safety and then seeing for the first time what happened to your home and all of your worldly belongings," Ardern said.