KENEDY, Texas (AP) — Authorities were searching early Thursday for seven inmates, including two convicted murderers, who took guards hostage, commandeered a cache of weapons then escaped from a south Texas prison in a stolen pickup truck.

Corrections officers, tracking dogs and Texas Rangers converged on the area outside the Connally Unit prison after the daring escape Wednesday. Two of the inmates were believed to be armed with 14 .357 Magnum pistols and 238 rounds of ammunition.

"We think this is a well-planned and well-executed escape that may have been under consideration by some of the inmates for several weeks," said Larry Todd, a spokesman for the Texas Department of Criminal Justice.

Todd said the inmates — all sentenced for violent crimes — took 11 employees and three other inmates hostage in the maintenance shop, where they worked as trusties. They then dressed in clothes taken from the civilian workers and raided a guard tower for weapons and ammunition.

They surprised two guards near the back gate and tied them up before making their getaway, Todd said. The white pickup was found later at a Wal-Mart store near Kenedy, about 50 miles southeast of San Antonio.

About 100 correctional officers — some with tracking dogs, some on horseback — searched nearby fields for the inmates. The Connally Unit has been locked down while prison workers and other inmates are questioned.

Though all the escapees were convicted of violent offenses, they had clean enough records behind bars to earn trusty status in the maintenance shop, Todd said. They were serving sentences ranging from 30 years to life in prison for kidnapping, robbery, sex assault, child abuse or murder.