At least 30 people were killed as twin bombs exploded in the central Nigerian city of Jos, underlining growing insecurity as Africa’s most populous country gears up for elections eight weeks away.

The bombs, believed to be the work of Islamists Boko Haram, came hours after the opposition candidate for February’s election was declared. The former military ruler Muhammadu Buhari will challenge the president, Goodluck Jonathan, in a campaign in which security is likely to be a major issue.

The two explosions, which went off minutes apart, unleashed growing anger over an insurgency that has left more than 10,000 dead this year. More than 118 people were killed when bombs went off in the same neighbourhood in May this year. A bomb blast on Wednesday killed four people in the northern city of Kano.

Muhammed Wase, a resident who rushed to the blast site near a bus station in Jos, said: “In the time it took for the police and military to reach the blast site, we had already evacuated two bodies. They didn’t help us at all when they arrived. We ordinary people on the streets are dying and nobody in government is interested.”

He said youths armed with sticks had initially squared up to security officials who they accused of not providing enough protection – an increasingly common occurrence as the number of attacks has risen sharply in the runup to the presidential polls.

Witnesses said at least 31 dead had been ferried to morgues across the city. City officials said they could not comment on the death toll.

Youths erected roadblocks across much of the city and began stopping cars in a city long used to self-policing. “Almost every street now has a roadblock. It’s not just checking the cars – they are checking everybody’s mobile phones and all their possessions,” said Muhammed Tanko, a local journalist. “People are just really scared and angry.”

Boko Haram is a Sunni jihadist group that has been waging a five-year insurgency to establish an Islamist state in northeast Nigeria. Jos, a religiously mixed hub in the centre of the country, has periodically erupted in sectarian violence, although many residents now feel that plays into the hands of the Islamists.