A car bomb attack near a Lashkargah sports stadium occurred when people had just returned from watching a wrestling game as part of Afghan New Year celebrations.
Aminullah Abed, the chief of the province's public health department in Helmand province, said the 12 killed and 40 wounded were received at a hospital in Lashkargah.
The Italian NGO Emergency said 35 wounded had been taken to hospital in the city.
"A car bomb blast happened at the entrance gate to the sports stadium in the first Police District of Lashkar Gah city," Helmand province's police spokesman told AFP.
Helmand governor spokesman Omar Zwak said at least 10 people had been killed and 37 others wounded.
"The explosion happened at a time when spectators were leaving the stadium after the wrestling match had finished," Zwak told AFP.