Mexico City ( CNN ) -- An explosion rocked the offices of Mexico 's state oil company Thursday , killing at least 25 people and injuring 101 , Mexico 's interior minister said . Dozens of people were trapped in the building after the explosion , Foro TV reported . It was unclear how many of them had been pulled to safety , or whether anyone remained stuck inside late Thursday , Interior Minister Miguel Angel Osorio Chong told reporters . More than five hours after the blast , rescuers had pulled at least one survivor from the rubble , Mexico 's president said in a Twitter post . Crews were still searching Thursday night for people who could be trapped in the Pemex office complex , which includes one of the city 's tallest skyscrapers . Watch : Office explosion rocks Mexico City . The explosion occurred in a basement and collapsed two floors of a building adjacent to the well-known tower , said Carlos Javier Rodriguez Jurado , one of the first paramedics to arrive at the scene . The explosion tore through the building `` from the inside out , '' he said , and rescuers found many people trapped . Six hours after the explosion , Rodriguez said people were likely still stuck in the rubble . It was unclear what caused the blast , and Mexico 's attorney general 's office is investigating , Pemex said in a statement . A large plume of smoke rose near the building after the explosion around 4 p.m. Thursday , and emergency crews swarmed the scene . `` 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 bodies from the rubble . Are you there ? Send us your photos , videos . `` Entering the building , we smelled a strong odor of gas , '' said Christopher Rangel , a paramedic and firefighter . Outside the building , frantic family members searched for loved ones , and shaken witnesses described the explosion . Mario Guzman said he was on the 10th floor of the tower when he felt `` a very strong blow . '' `` We felt like the whole building was going to collapse , '' he told CNNMexico . Images from the scene showed emergency rescue teams carrying people on stretchers . Authorities said helicopters carried some of the wounded to hospitals . At least 14 people were hospitalized with injuries , and two of them were in serious condition , the state-run Notimex news agency reported . Mexican President Enrique Pena Nieto surveyed the damage Thursday night , along with Osorio Chong and Mexico City 's mayor . Pena Nieto cautioned against speculating over what caused the blast , and said authorities would be closely investigating . Thousands of people work at the Pemex headquarters , which includes a 54-story building that is nearly 700 feet tall . The explosion occurred in an annex building just to the east of the tower , Foreign Minister Jose Antonio Meade said . Officials evacuated the complex and operations will cease there until further notice , the company said . The state oil company 's director , who was on a business trip in South Korea this week , said in a Twitter post that he would return to Mexico immediately . `` We will get to the bottom of the causes in close coordination with the authorities , '' Pemex Director General Emilio Lozoya Austin said . `` At this time , attending to the injured is the priority . '' Federal troops and rescue dogs were aiding in search efforts late Thursday night . As they combed through the rubble , a Pemex executive 's cell phone rang , Rangel said . A man on the other end of the line said he was still trapped , and started to describe his location to rescuers . `` Unfortunately , we lost communication with him , '' Rangel said . When they called back , his phone did n't ring . CNN en EspaÃ±ol 's Krupskaia Alis reported from Mexico City . CNN 's Catherine E. Shoichet reported from Atlanta . CNN 's Rafael Romo , Edwin Mesa , Christine Theodorou , Rey Rodriguez , Rene Hernandez and CNNMexico 's Arturo Ascencion and Javier Rodriguez contributed to this report .
NEW : 25 people were killed and more than 100 are injured , interior ministry says . The explosion collapsed two floors of an office building , paramedics say . Rescuers have pulled a helicopter from the rubble , Mexico 's president says . Crews are searching for people trapped in the building .