Flash flooding caused by torrential rains killed at least six people, including a 3-year-old child, in northern West Virginia and rescue crews were still searching for several missing people, officials said. Authorities were assessing damage to roads, bridges, natural gas lines and other infrastructure.

Officials said 2.5 to 4 inches of rain fell in parts of Wheeling and Ohio County within about half an hour on Saturday night. The unexpected deluge overwhelmed local waterways and infrastructure and submerged vehicles in small towns east of the Ohio River, including in Triadelphia and Valley Grove, . 

In Fairmont, a city nearly 100 miles from Wheeling, severe flooding led to multiple water rescues Sunday afternoon, , including at an apartment building in Marion County.

A city spokesperson told CBS News that an apartment building had partially collapsed, but it wasn't immediately clear how many people were impacted. Residents were evacuated to Fairmont State University's campus, the spokesperson said.

West Virginia Gov. Patrick Morrisey said Sunday night that three residents were also missing, and more rain and flooding were possible. The governor said at an earlier news conference that he's working closely with authorities from FEMA.

Monday morning, the death toll had risen to six.

Authorities said vehicles were swept into swollen creeks, some people sought safety in trees and a mobile home caught fire. First responders successfully completed 19 swift water rescues, Morrisey said.

"It happened so quickly"

"We almost immediately started getting 911 calls for rescue of people being trapped," Lou Vargo, Ohio County's emergency management director, said at a news conference Sunday. "During this time, we had major infrastructure damage to roads, bridges, and highways, where we couldn't respond to a lot of incidents. So we were delayed in getting there because there was just so much damage."

Vargo added: "It happened so quickly and so fast. … I've been doing this for 35 years. I've seen major floods here in the city and the county. I've never seen anything like this."

Jim Blazier, the fire chief in Wheeling in the state's northern panhandle, said crews performed rescue operations into Sunday's early morning hours. He said first responders regrouped Sunday morning and were focused on an area from the Ohio state line across the Ohio River to Wheeling Creek.

"We're searching the banks, we're searching submerged vehicles, any debris we find along the trail and so forth," Blazier said. "We're using drones, search dogs and swift water personnel, and we have teams organized that are searching sectors that we're trying to recover anybody that's missing."

There were about 2,500 power outages in the county as of Sunday afternoon, the governor said. Restoration efforts were hampered by natural gas leaks that have to be fixed first, officials said.

"Please — stay off the roads," Gov. Morrisey warned residents. "Do not underestimate the strength and speed of these floods. Pray for our friends and neighbors during this challenging time for our state."

Morrisey has declared a state of emergency in both Ohio and Marion County. He said state police and other state officials were responding, and he directed the National Guard to provide any needed assistance.

"Please keep this community in your prayers," Morrisey said in a statement Sunday. "More storms are expected in the region today. Please follow all directives from local and state emergency management officials and do not attempt to drive through flooded roads."

The West Virginia rains followed heavy downpours in San Antonio on Thursday that killed 13 people. More than 7 inches of rain fell over several hours in the Texas city, causing fast-rising floodwaters to carry more than a dozen cars into a creek.

• West Virginia
• Severe Weather
• Flood
• Flash Flooding