ABUJA, Nigeria (AP) — Two people died and 77 others were injured after a massive blast rocked more than a dozen buildings in one of Nigeria’s largest cities Tuesday night, the governor said Wednesday, as rescue workers dug through the rubble in search of those feared trapped.

Residents in the southwestern state of Oyo’s densely populated Ibadan city heard a loud blast at about 7:45 p.m., causing panic as many fled their homes. By Wednesday morning, security forces cordoned off the area while medical personnel and ambulances were on standby as rescue efforts intensified.

Preliminary investigations showed the blast was caused by explosives stored for use in illegal mining operations, Oyo Gov. Seyi Makinde told reporters after visiting the site in the Bodija area of Ibadan.

“We have already deployed first responders and all relevant agencies within Oyo state to carry out comprehensive search and rescue operations,” Makinde said, describing the damage as “devastating.”

Illegal mining in mineral-rich Nigeria is common and has been a major concern for authorities. However, it is mostly done in remote areas where arrests are difficult and where safety procedures are rarely followed.

It was not immediately clear who stored the explosives, and no arrest has been announced. “The investigations are ongoing (and) all those found culpable for this will be brought to book,” Gov. Makinde said.

Most of the 77 injured were already discharged, the governor said, promising to cover the medical bills of others still being admitted and to provide temporary accommodation for those whose houses were affected.