(http://news.bbcimg.co.uk/media/images/79899000/png/_79899764_nigeria_gombe_bauchi_464.png) Red Cross official Abubakar Adamu Gombe told the BBC Hausa service that body parts lay scattered at the site of the blast in Gombe.
Government official Mato Yakubu said the explosion occurred, as people were climbing on to a nearby bus at the Dukku bus park, AFP news agency reports.
Mr Gombe said he expected the number of people killed by the explosion to rise.
Eighteen people had been rushed to hospital with serious injuries, he added.
At least three people were killed in a bomb attack at another bus station in Gombe city on 31 October.
(http://news.bbcimg.co.uk/media/images/77154000/jpg/_77154888_77153742.jpg) Boko Haram is fighting to create an Islamic state Gombe state shares a border with Bauchi state as well as Adamawa, Borno and Yobe, the three Nigerian states worst-affected by the insurgency and which have been under emergency rule since last year.
The explosion in Bauchi city had caused a huge fire, and there were "heavy casualties", the Red Cross said.
On Sunday, Cameroon's military said it had dismantled a training camp run by Boko Haram in the Guirvidig locality near its border with north-eastern Nigeria.
Soldiers captured 45 trainers and 84 children between the ages of seven and 15 who were undergoing training, a spokesman for the Ministry of Defence, Lieutenant Colonel Didier Badjecks, told the Reuters news agency.
He said "many more" had been killed in the raid.
Boko Haram launched its insurgency in Nigeria in 2009 to create an Islamic state in the region.
At least 2,000 civilians have been killed by the group in Nigeria this year.
The kidnapping of more than 200 schoolgirls by Boko Haram in April from the town of Chibok in Borno state sparked international outrage.
Source: BBC