Police said State Highway 2 had also been closed south of Waihi because of a slip at Athenree Gorge.
Emergency management officer Greg Ryan said the Piako, Waihou and Waitoa rivers were also expected to become swollen over coming days.
"We advise farmers to move stock to higher ground if necessary and for all residents to stay up to date with information regarding river levels.
"People need to be aware of the potential for inundation of flood plains, surface flooding generally and for transport links to be disrupted."
Mr Ryan said flooding could threaten Waikato residents.
"It looks as though we're in for a few very wet days on top of what has already been a very wet July, so risks will certainly be elevated this week."
The AA said several roads around Coromandel had been cut off due to flooding today.
Hikuai Settlement Rd and Cobham Dr between Wellington Rd and Miramar Ave were impassable because of flooding, while Tapu-Coroglen Rd was blocked by landslips.
Earlier, heavy rain led to traffic problems but caused little damage in Auckland.
Police said a tree has fallen over on Huia Rd in the Auckland suburb of Titirangi, blocking traffic in both directions.
Council staff are working to the remove the tree as soon as possible, but it may be a few hours before the road reopens.
Police appealed for motorists to drive with caution as the blocked road is obscured by a bend.
Fire Service Northern Communications said there were no weather-related call outs overnight.
A severe weather watch for the area was now lifted.
