Quetta, Pakistan - A bomb planted under a tea stall at a railway station in southwestern Pakistan has killed seven people, including a child, and wounded 18 others, police said on Thursday.

The explosion on Wednesday 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 it arrived at Sibi station, officials said.

“A total of seven people have been killed and 18 wounded,” senior police official Qazi Hussain Ahmad told AFP on Thursday, updating an earlier toll of five dead and 15 injured.

Local administration official Shahid Saleem told AFP that the bomb exploded at around 11:30 pm.

Authorities warned that with many of the injured in a serious condition the death toll could rise further, but that the 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 600 kilometres southwest of Islamabad, in Pakistan's southwestern province of Baluchistan which is blighted by a separatist insurgency and sectarian and Taliban violence.

There was no immediate claim of responsibility for the attack.

Pakistani train travellers are usually among the country's least well-off, and often face laborious journeys in ageing carriages, along a network 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 a 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 Sunnis and Shiites, who account for around 20 percent of the population, that has left thousands of people dead since the late 1980s. - Sapa-AFP