About 500 people in the village of Perth-Andover were ordered to leave for higher ground Friday morning after the river spilled its banks, floodings streets and basements.
The province's Emergency Measures Organization said another 50 or so people were forced from their homes overnight on the nearby Tobique First Nation as a precaution, though there was no flooding reported.
"Everybody is safe," Lisa Harrity, a spokeswoman for EMO, said Saturday.
"The water is starting to decline in the region, very slowly at this point. There is an ice jam still in place."
The organization said water levels in Perth-Andover were still above flood stage in the afternoon and a local state of emergency declared Friday remained in effect.
The evacuation order affected about 10 streets along a four-kilometre section of the river.
Harrity said given the unpredictable nature of the river, it was too early to say when the order would be lifted as streets were still flooded.
"We obviously want to get people back into their homes as quickly as possible," she said from Fredericton.
Harrity said inspectors were on standby to assess homes for damage as soon as it was safe to do so. In the meantime, the Red Cross had set up two centres for evacuees in the village.
Emma Lavoie-Evans, a disaster management worker with the organization, said some evacuees were coming in for meals or to use the phone. A number of firefighters spent the night on cots, though evacuees were mostly staying with loved ones or in hotels.
"People were shocked by how fast the water rose and I think everybody is still a bit in disbelief," Lavoie-Evans said from Perth-Andover.
"But the community has been very supportive. We've had a lot of people drop by looking to give donations or volunteer."
The river has been rising because of unseasonably hot weather that caused a rapid snowmelt and an ice jam downriver.
Harrity said officials were cautiously optimistic, particularly because there was no precipitation in the forecast for the next few days.
"It's just a waiting game at this point," she said. "With ice jam flooding, by its nature it goes up very quickly and once it does start to break up, it's likely that it will go down very quickly."
Meanwhile, in the capital Fredericton, water levels were just above flood stage along the St. John River.
There was some flooding reported along a walking trail that borders the river, but the province said water levels were expected to decline by Sunday.
Water levels were also above flood stage in Woodstock, a community about 100 kilometres northwest of Fredericton. Those levels were also expected to decline gradually on Sunday.
In the meantime, residents were being reminded to avoid low-lying areas.
The province issued a water level warning Friday for the northwestern community of Clair, but Harrity said levels were below flood stage on Saturday.
She said levels along the Nashwaak River were also below flood stage.