( CNN ) -- A day after an explosion rocked its offices in Mexico City , Mexico 's state-run oil giant Pemex says it 's too early to speculate on the cause of the deadly blast . At least 33 people -- mostly women -- were killed in the explosion , Pemex chief Emilio Lozoya said at a news conference Friday . More than 100 were injured , including 52 who remain hospitalized . Watch : Blast rocks Mexico City . Lozoya was asked if he believed Pemex , the powerful but often criticized state oil monopoly , was the target of a bombing , but he declined to speculate . Experts from Mexico and abroad are investigating the scene to determine the cause , he said . Mexican Attorney General Jesus Murillo Karam similarly refused to rule out possibilities . `` We have experts in everything , absolutely everything , '' he told reporters , adding that investigations are under way to determine whether the blast was the result of an accident or an attack . Some witnesses have reported smelling a strong odor of gas after the blast . It is a complicated investigation that `` can not be explained in a few hours , '' Lozoya said . The priority , Lozoya said , is providing support to the victims ' families and rescuing anyone who may remain trapped . Mexican President Enrique Pena Nieto visited victims in the hospital Friday , offering condolences and promising help . The explosion happened Thursday afternoon at an administrative building in the Pemex office complex . `` People were screaming . ... You could see pieces of the wall falling to the ground , '' said Joaquin Borrell Valenzuela , an attorney for the Pemex comptroller 's office , who was in a courtyard outside the building at the time of the blast . Paramedics quickly arrived and started pulling people from the rubble . Thousands of people work at the Pemex headquarters , which includes a 54-story building that is nearly 700 feet tall . The annex where the explosion happened is adjacent to the tower . The oil company 's production capabilities have not been harmed , and operations and oil production will continue Friday as normal , Lozoya said . Employees at the Pemex annex said that the basement of the building , where he explosion is believed to have originated , housed a water treatment facility , storage areas and archives . The first floor , which also was heavily damaged , is where the company 's human resources team worked . One employee , Silvia Hernandez , recounted how she was finishing up her workday at another building and standing in line to clock out when she heard a blast . `` I saw the explosion of glass , people bleeding ; it was something very shocking , '' she said . `` I ca n't say more because the memory makes me nervous . I was terrified , anxious . '' A bridge that connected her building with the annex collapsed , likely trapping employees , she said . Another employee , who declined to give his name for fear of retribution , spoke about his failed attempt to locate his brother within the rubble . The man smoked cigarette after cigarette in the predawn hours of Friday as he waited at the medical examiner 's office to claim his brother 's body . More than 100 relatives waited outside the offices with him . The man said he was among the employees who began rescue efforts in the immediate aftermath of the explosion . He knew his brother worked in the human resources area , which had been damaged , so the man covered his face with a rag and ran there to search for him . The man said he removed debris and helped rescue others , but never reached his brother . By then , professional rescuers arrived and took over the job of looking for survivors . CNNMexico 's Juan Pablo Mayorga and Arturo AscenciÃ³n contributed to this report .
NEW : The country 's attorney general similarly refuses to rule out possibilities . Mexico : President Enrique Pena personally visits victims in the hospital . The death toll rises to 33 . Employee : ` ` I saw the explosion of gunfire , people bleeding ; ... I was terrified ''