KARACHI, Pakistan — At least 42 people were killed Sunday morning in southern Pakistan after a bus slammed into a tractor-trailer in one of the worst traffic accidents in this country in recent years, officials and rescue workers said.

The crash took place on a busy highway in the Sukkur district of southern Sindh Province. The bus, which departed from the Dera Ghazi Khan district of Punjab Province, collided head-on with a tractor-trailer traveling in the opposite direction, said Sharjeel Kharal, the deputy inspector general of the Sindh Police. The driver of the bus lost control of his vehicle, which had seats for 60 but was overloaded and carrying 75 passengers, police officials said.

The dead included 14 women and 13 children, all from the Dera Ghazi Khan district, Mr. Kharal said. The crash also left 30 people injured.

Some of the injured blamed the bus driver for reckless driving and held him responsible for the crash. The driver tried to pass another vehicle on a narrow road but ran into the tractor-trailer, the passengers said.