More than 500 people are missing and at least 4 people have died, with another victim believed to be dead, after flash floods hit Colorado.

Many residents are still stranded in their homes as rescue workers try to reach them. Boulder county officials fear rescue attempts will be hampered by the extra 4in of rain due on Sunday.

Authorities who still haven’t reached all the stranded victims of floods in northeastern Colorado are bracing for a new round of storms on Sunday.

Already it is estimated that it will cost $150 million to repair more than 100 miles of road and at least 20 bridges that have been washed away.

County transportation director George Gerstle told CNN the repair bill is likely to be 10 to 15 the annual budget.

A sheriff’s office spokesman said hundreds of people were unaccounted for, but added that some residents may have reached safety but not been able to contact relatives to tell them.

Boulder County Sheriff Joe Pelle said authorities had to be “realistic” about the chances that the death toll will rise.

With the rain never seeming to end and the waters continuing to rise, more than 4,000 people near Boulder, Colorado, have been evacuated as nearby Milliken has been surrounded by water and turned into an island, according to reports.

More than 500 people are missing and at least 4 people have died, with another victim believed to be dead, after flash floods hit Colorado

The reality of what is becoming a long-term disaster is setting in, flooding has affected parts of a 4,500-square-mile area almost the size of Connecticut.

In the most recent developments, people are stranded in Milliken after the main road out of town was washed away by raging floodwaters, according to CBS Denver. As the devastating rapids rise, they wash away more of the road, and flood ever closer to even more homes.

“The fire department said Milliken is an island but I found a way out,” Jorge Garza told the station.

A CBS Denver helicopter flying over the town spotted a family of three and their dog being rescued from menacing waters via a motorized raft.

“[Milliken] has turned into a lake with campers, fields and cars submerged,” the station further reported.

172 people are unaccounted for, Boulder County officials told KDVR.

As rescuers broke through to flood-ravaged Colorado towns, they issued a stern warning Saturday to anyone thinking of staying behind: “Leave now or be prepared to endure weeks without electricity, running water and basic supplies.”

Authorities made clear that residents who chose not to leave might not get another chance for a while.

“We’re not trying to force anyone from their home. We’re not trying to be forceful, but we’re trying to be very factual and definitive about the consequences of their decision, and we hope that they will come down,” Boulder County Sheriff Joe Pelle said.

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