It could be weeks or even months before some residents are allowed back, said Cache Creek Mayor John Ranta on Sunday.
So far about 40 residents have been ordered to evacuate in the village of about 1,000 located 80 kilometres west of Kamloops, B.C., he added. Another 80 are on evacuation alert.
"We'll do our best to ensure that they're allowed back as quickly as possible if (their homes) are deemed to be safe," he said.
The order to evacuate will keep people away until crews are able to assess the stability of the slopes above residences that are deemed at risk.
As of Sunday afternoon about 50 homes had been abandoned and nearly 100 people had registered at the emergency operations centre, said Ranta.
Rainfall levels had topped 26 millimetres in a single hour on Saturday, sending detritus-strewn mud and water pouring through the community's streets and shutting down two highways.
Ranta said he was in his car when the storm began shortly after 4 p.m. on Saturday, and that by 6:30 p.m. the village was devastated.
"It started off as a trickle that was going down the storm sewers, to a river that was running down the road with debris floating along," he said, describing the intensity of the rainfall as "unbelievable."
"It was raining just like you can't describe — rain combined with hail, coming down like the sky was falling."
Declaring a state of emergency could mean more financial support from the province for rebuilding on the heels of the disaster — especially important given that Ranta believes few homeowners have flood insurance.
Charlene Milward's 2,000-square-foot home is one such residence, where insurance may not cover the damage after her home was shoved off its foundation and her basement was completely filled with mud.
"She's pretty numb right now," said her mother Cheryl. "She's in disbelief."
Ranta called on the province and emergency response agencies to step in to help in situations such as this.
"Imagine how devastating it would be to lose your home to a rainfall event and not have insurance coverage," he said.
On Sunday, B.C. Premier Christy Clark tweeted her support for residents affected by the flooding.
Local Member of the Legislative Assembly Jackie Tegart said the situation is especially devastating for a semi-desert settlement like Cache Creek, which is unaccustomed to high levels of rainfall. But she noted that the community was banding together to recover.
"Small communities help each other," said Tegart. "And certainly from what I've seen and heard from people on the ground that's exactly what's happening."
Environment Canada said a severe thunderstorm watch remained in effect for Kamloops, the Okanagan and the Shuswap Sunday evening.
— By Geordon Omand in Vancouver
— Follow @gwomand on Twitter