The number of deaths caused by two back-to-back tornadoes which smashed the southern state of Alabama in the United States on Sunday is likely to rise.

The search for dozens of missing people was focussed in the area around Beauregard, about 100km east of Alabama’s capital Montgomery, where so far 23 people are known to have died in the deadliest US twisters in nearly six years.

Rescue crews using dogs and drones searched for victims amid splintered lumber and twisted metal, while volunteers used chain saws to clear paths for emergency workers.

“It looks almost as if someone took a giant knife and scraped the ground,” Sheriff Jay Jones of Lee County told the AFP news agency.

“We have several people who are still unaccounted for,” Jones said. “Unfortunately, we anticipate the number of fatalities may rise.”

A powerful EF-4 “monster tornado” was blamed for most of the destruction on a path about 39km long, meteorologist Chris Darden said. The deadliest, an EF-5, killed 24 people in Oklahoma in 2013.

More than 6,000 homes were left without power in Alabama, according to PowerOutage.us, while 16,000 suffered outages in neighbouring Georgia.

The twisters were part of a powerful storm system that slashed its way across the Deep South, spawning numerous tornado warnings in Georgia, South Carolina and Florida.

An early March tornado outbreak in the Alabama-Mississippi area is usual, experts said.