The bomb, planted close to the Frontier Corps (FC) checkpoint went off early Saturday when soldiers reached the site for daily duty in Quetta, the main town of oil and gas rich Baluchistan province, senior police official Abdul Waheed Khattak told AFP.
"It was an IED (improvised explosive device) which exploded the moment soldiers reached the checkpoint," Khattak said.
He added the blast killed one soldier and wounded four others including a teenager passing the site at the time of the explosion.
"(The) condition of another soldier is also critical," Khattak said.
Sajjad Ahmad, a senior official from FC, confirmed the attack and casualties.
Thousands of paramilitary troops are deployed in troubled areas of the country to carry out security checks and to help police in maintaining law and order.
No group has yet claimed responsibility for the latest attack but Baluch separatists demanding greater autonomy have been waging an insurgency for years and the province is also riven by sectarian strife.