(CNN) -- Five blasts went off in the Nigerian city of Jos Friday night as residents were celebrating Christmas Eve, leaving 31 dead, a regional government official said. 

Choji Gyang, a special adviser to the governor of Nigeria's Plateau state, said two bombs went off in the Angwa Rukuba area of Jos. Within five to 20 minutes, three more blasts happened in the area of Kabong, he said. 

"We have a lot of casualties and are struggling to cope," Gyang said. 

Hassan John, a Jos resident and journalist with the media department of the Anglican Diocese of Jos, had just come out of church about 7 p.m. (1 p.m. ET) when he heard the sound of the first explosion. He rushed to the site, which he described as a beer parlor frequented by locals. 

"By the time I got there, there were women crying, people screaming. It was all chaos, people were screaming, blood everywhere." 

"I counted eight corpses all over, seven in the building," John said. He added that a second blast went off within a couple of minutes after the first one. "We cannot say if there are more bodies under the rubble because it was dark," John said. 

Gyang, who is special adviser on religious affairs to the governor, said it was unclear who set off the blasts or whether they were related. 

"It was Christmas Eve, lots of activities was going on. People were still preparing for Christmas, lots of people were coming into town. A blast went off, those around the area -- some were killed, some injured and the houses and cars caught fire," Gyang said. He said he received reports of "a lot of dead bodies." 
Who is responsible?
it was unclear who set off the blasts