The threat of a storm and record flooding in British Columbia's Okanagan region has residents trying to protect homes that could be evacuated.

Parts of the area that were flooded last weekend are so saturated that water levels will quickly rise with little rain, said Adrian Nieoczym, information officer with the Regional District of the Central Okanagan.

He said Environment Canada has forecast a severe thunderstorm that could bring 25 millimetres of rain by Friday morning, but snow melt prompted by warm weather is expected to worsen conditions.

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"The possibility is that we could have a one-in-200-year flooding event," Nieoczym said after the regional district issued a news release advising residents that the risk of flooding within hours was very high.

"There are two creeks that run through Kelowna that we're most concerned about, that's Mission Creek and Mill Creek," he said.

"Judging by the number of calls we're getting, I'd say people are quite concerned," he said, adding residents are asking about ways to protect their property.

Crews were building up dikes as sand and sandbags were dropped off at several locations with help from 112 people from the wildfire service, Nieoczym said.

The main communities under threat are Peachland, Kelowna, West Kelowna, West Bank, Lake Country and Vernon.

An emergency services reception area has opened in Kelowna for evacuees to register and get vouchers for accommodation, Nieoczym said.

Kelowna Mayor Colin Basran posted a Facebook statement late Wednesday describing expected water levels as "unlike anything we have ever seen in our community."

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"This is the time now where, as a community, we need to come together and look after each other," he said.

The regional district's suburban and rural planning manager Todd Cashin said reservoirs around Kelowna were full and all area lakes were at capacity.

"Our cup is full, the bucket is full, there's really nowhere more for the rain to go except over creek banks and up onto people's properties along our lakes," he said.

The River Forecast Centre posted a flood watch for the Salmon River in Shuswap, while high streamflow advisories covered most waterways across the southern and southeastern parts of the province.

High streamflow advisories were also in place for northern parts of the province, including the Bulkley Valley, northeast B.C., and the Peace region.

Severe thunderstorm watches were issued for parts of the central and southern Interior, with the potential for strong winds, large hail and heavy rain.

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That has added to the concerns of hundreds of residents on evacuation order and thousands who have been told to be ready to leave home on short notice.

The Insurance Corporation of British Columbia issued a statement urging drivers to find high ground to temporarily store vehicles away from flooded areas, adding rising waters can quickly wash out roads and bridges.