Residents of B.C.'s Central Coast and northern Vancouver Island are bracing for more flooding as forecasters predict 40 to 70 millimetres of rain could fall across the region by Tuesday.

A weekend deluge washed out roads and cut off several communities near Bella Coola and Port Hardy after more than 200 millimetres of rain fell on some coastal areas north of Vancouver, creating some of the worst flooding on record.

At least 120 people were still out of their homes on Monday morning and as many as 600 remained stranded by the floodwaters, said Steven Waugh with the Emergency Operations Centre in Bella Coola.

"We had a bit of a reprieve yesterday because the rain stopped and the waters went down yesterday. And we did as much as we could to secure people and make sure they were in a safe spot, because we knew there was another fairly strong event coming and it's now happening," said Waugh on Monday.

"So our intent right now is to continue doing as much as we can as our transportation links are a little bit more open in the valley, but by this afternoon we expect to be cut off again," he said.

There's been major damage to highways and infrastructure on the Central Coast, leaving boats and helicopters as the only way in and out of the region. A 100-kilometre stretch of Highway 20 was closed between Bella Coola and Anahim Lake, and the local airport runway is flooded.

"Our airport is also out. The dike broke above the airport and the runway is out of service. So we're pretty much cut off … right now," said Waugh.

The villages of Firvale and Hagensborg on the Central Coast were hardest hit, and residents have gathered at a local emergency operations centre, said Theresa Hood, who works at the band office of the Nuxalk First Nation.

"They've asked us to stay home, just to go out when there's an emergency, because it's so bad. But Highway 20 is washed out and it's going to take a lot of time to get that repaired. We're looking at four to eight weeks to get it repaired so our supplies are going to run out pretty quick," she said.

Waugh said they had expected heavy rains, but the flooding took them by surprise.

"We had no snow in the mountains whatsoever and our rivers were low. They're very empty because it's been so dry. So I believe that there may well be a factor in that the forest fires and the mountain pine beetles have dropped the water-holding capacity of the soils, reduced that in the upper slopes. So we're getting more water down in the valley than we have in the past," he said.

Vancouver Island communities affected

There was also major flooding on the northern end of Vancouver Island in and around the communities of Port Hardy, Port Alice and Holberg over the weekend, but the flood waters there appeared to be receding by Monday morning.

RCMP Sgt. Phil Lue said the region is no longer being pelted by rain and flood water has started to recede. Residents of Port Alice and Kingcome have been told they can return home.

About 70 trailers and a dozen homes were evacuated after a mudslide Friday washed out the main road in the village of Port Alice, and boats were being used to ferry people in and out of Holberg over the weekend.

In nearby Kingcome Inlet on the mainland, approximately 70 people were airlifted to safety Saturday after flood waters continued to rise.

Port Hardy Mayor Bev Parnham declared a state of local emergency on Saturday. She plans to meet with the provincial officials on Monday to ask for help for residents whose homes were damaged by floodwaters but who are not covered by private insurance.

While Port Hardy was not cut off, residents there suffered the most flood damage, said Lue.

"Nobody was evacuated from Port Hardy," he said. "Some people drove from their homes to the community centre and reported that 'My house is flooded and damaged,' but nobody was really displaced from their homes."

On Monday morning, emergency co-ordinators dispatched equipment to clean up the mudslide that closed the road to Port Alice and repair the route to Port McNeill, Zeballos and Holberg.