A bomb planted under a tea stall at a railway station in southwestern Pakistan killed at least five people, including a child, and wounded 15 others late Wednesday, police said.
The explosion appeared to target the express train from the southwestern city of Quetta en route to Rawalpindi, the capital's twin city to the north, as the locomotive came into platform two at Sibi station, officials said.
"The blast happened at around 11:30 pm (1830 GMT). Five people are dead and at least 15 people are injured, of which eight are in a critical condition," local administration official Shahid Saleem told AFP.
Officials warned that the death toll could rise further with so many in a serious condition, but said the number of casualties would have been greater had the train been fully on the platform at the time of the attack.
"The dead include a railway police constable and a child, aged six or seven," Saleem said.
Sibi is a major railway junction about 400 miles (600 kilometres) southwest of Islamabad and is part of Pakistan's southwestern province Baluchistan, which suffers from separatist insurgency, sectarian and Taliban violence.
There was no immediate claim of responsibility for the attack. In Pakistan it is generally the least well off who choose to travel by train, an often laborious journey on ageing carriages that is prone to serious delays.
Local official Qamar Maqsood said most of the victims had been standing on the platform when the bomb exploded.
Baluchistan is rich in oil and gas, but remains one of the most deprived areas of Pakistan. Rights activists have accused the military of mass arrests and extra-judicial executions in its bid to put down the separatist insurgency.
This month, UN human rights chief Navi Pillay voiced concern about "very grave" rights violations during Pakistani military operations.
Baluch rebels rose up in 2004, demanding political autonomy and a greater share of profits from the oil, gas and mineral resources in the region.
The province has also been a flashpoint for violence between two sectors, who account for around 20 percent of the population, that has left thousands of people dead since the late 1980s.