It was the second attack this week after the former rebel movement Renamo on Monday declared that a 1992 peace deal was over after government forces took over their military base in central Mozambique's Gorongosa mountains.
"Armed men came out of the woods, opened fire and hit the driver in the forehead or the face," said Felisberta Moutinho, a survivor of the attack.
A source at the Muxungue rural hospital confirmed one dead and at least nine wounded. Moutinho said 10 were wounded.
Renamo spokesmen declined to comment.
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A group of cars had been travelling northbound from the Machanga district towards the coastal city Beira when the gunmen attacked three vehicles.
"They kept shooting at the passengers. We left the bus and fled. Some fled through the windows, others were hit by bullets," Moutinho told AFP.
She said she ran into the woods with her two children until she found a group of police vehicles.
"They stole all our things and then set fire to the bus."
Four people were seriously wounded and six others had light injuries, she said.
"Some children have serious wounds and are now in hospital," Moutinho said.
The attack came a day after Renamo announced its leader's right-hand man and member of parliament Armindo Milaco had been killed by a howitzer in Monday's assault on the group's base.
Milaco, a former child soldier, was head of national recruitment for the movement.
A day after the base fell, armed gunmen assaulted a police station in nearby Maringue district.
It became the official opposition party after a 1992 peace agreement, but has lost every national election since.
Last November Renamo leader Afonso Dhlakama returned to his bush camp Sathundjira near the Gorongosa mountains, saying he would retrain his soldiers for a revolution.