(CNN) -- A massive crash sent 19 people to hospitals as thick fog and ice covered a Virginia highway Sunday.
The crash happened around 4:30 a.m. on the eastbound lanes of Interstate 64 near the Nelson-Augusta county lines, Virginia State Police spokeswoman Corinne Geller said.
"Heavy fog and icy road conditions are to blame," Geller said.
The driver of a tractor-trailer lost control, and the semi truck filled with mail overturned, state police said.
A nearby charter bus wasn't able to avoid the overturned semi and struck it.
"The impact of the crash split the tractor-trailer in half," Geller said. "The bus ran off the right side of the highway and came to rest against the guardrail."
More than 20 people were on the Silver Lining Charters & Tours bus, police said.
At least 20 people were taken to UVA Medical Center, the hospital said, and four of them were admitted.
The bus driver, Andrew L. Burruss, and the driver of the semi truck, James Proffitt, were among the injured.
No fatalities were reported. The injuries of those hospitalized range from serious to minor.
At least seven minor crashes followed in the same lanes as the major crash, state police said. No one was injured in those minor crashes.
The Virginia State Police Motor Carrier Safety Team is assisting with the investigation. The US Postal Inspection Service also responded to the scene because the tractor-trailer was loaded with mail.
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