A former nurse who is in prison for the killing of a toddler in 1982 has been charged with murder over the death of an infant a year earlier.

Prosecutors say a Texas nurse who is in prison for the 1984 killing of a toddler and faces new charges over the 1981 death of an infant is suspected of killing as many as 60 children who were in her care around that time.

The police chief of a small south Texas town was shot dead during a traffic stop on Saturday, a county sheriff said.