Wairoa residents received an emergency alert on Thursday night as floodwaters began to rise in low-lying areas.People between Outram and Grant Streets, and Kopu Road and Apatu Street were advised to leave immediately, taking essential items and pets.Earlier Wairoa District Council said floodwater was beginning to come across Kopu Road and the road was closed in the Sturdee Street area.It comes amid an orange heavy rain warning for the ranges of Hawke's Bay, north of Napier, that is in place until 9am Friday.MetService said: "Expect 100 to 130mm of rain on top of what has already fallen. Peak rates of 10 to 20 mmh expected today."The council earlier warned residents to be ready to leave at a moment's notice - concerned about the lower catchment of the Wairoa River.It said police will be door knocking properties in the area to ensure residents are aware of the changing conditions and to assist anyone who may need to evacuate."If you live in or near this area, please be prepared to leave immediately if advised to do so. If you feel unsafe, do not wait. Move to higher ground, stay with family or friends, or head to the Wairoa War Memorial Hall, which is open as an evacuation centre."People are also advised to avoid travelling through flooded roads.Following discussions with its flood modellers on Thursday evening, the council said there are increasing concerns that river levels may rise significantly overnight.At this time, its concern is for the lower catchment of the Wairoa River."While the Wairoa River mouth is open, outgoing water and rising flow is competing against large 3m-4m swells coming in from the coast," it said."More water is also expected to flow into the Wairoa River from the upper catchments, with further heavy rain forecast overnight."High tide was expected around 12.47am on Friday, with intense periods of rain between now and 3am.The council was encouraging people who lived in a low-lying area to prepare now."Have essential items ready, know where you will go if you need to leave, and be ready to move quickly if conditions change.""If you are concerned about your safety, please don't wait," it said."Move now to higher ground or stay with family or friends in a safe location."Mayor Craig Little said the emergency operations centre has been stood up and will be monitoring the situation through the night.A heavy rain warning is in place until tomorrow morning for the ranges of Hawke's Bay north of Napier.