Riot police have clashed with striking teachers during an operation to clear an occupied Mexico City square.
The police used tear gas and water cannons to remove the protesters from the city’s main square, the Zocalo.
Striking teachers had been camped out there for weeks. Some responded with petrol bombs as police moved in after a government deadline passed.
The teachers have been demanding changes to education reforms approved by President Enrique Pena Nieto.
The authorities said they wanted to clear the Zocalo for the Independence Day celebrations at the weekend.
Riot police have clashed with striking teachers during an operation to clear occupied Mexico City’s Zocalo Square
Most of the protesters left peacefully by Friday’s deadline. But some stayed on, and police backed by armored vehicles and helicopters clashed with missile-throwing protesters on the square and in nearby streets.
Officers tore down the teachers’ temporary shelters and put out small fires started by the demonstrators and made a number of arrests.
Some of the demonstrators were thought to be radical anti-government activists who were not necessarily associated with the teachers union.
The educations reforms introduced by the government include performance-related tests for teachers.
Critics accuse Mexico’s teachers’ unions of being corrupt and having too much control over job allocation.
Last week, thousands of its members protested outside the Senate in an attempt to disrupt the passing of the bill, which had already been approved by the Chamber of Deputies.
The government has argued that union control over teaching jobs has contributed to corruption, which has seen poorly trained teachers promoted over more qualified colleagues.
At least 25 people were killed by a blast in Mexico City at the headquarters of the state oil company, Pemex, the interior minister has said.
Another 100 people were injured and an unknown number are trapped in rubble at the base of the 54-storey tower. The search for survivors continues.
The cause of the blast is under investigation, Pemex says.
Last September, 30 people died in an explosion at a Pemex gas plant in northern Mexico.
Thursday’s explosion in the lower floors of the building happened as shifts were changing in the afternoon, making the area particularly crowded.
Television pictures showed debris from the blast spread out on to the street in front of the building, and Red Cross ambulances on the scene attending to the injured.
Hundreds of rescuers helped by dogs are searching the building for around 30 people thought to be trapped inside.
Police have cordoned off the streets around the building, which is located in a busy commercial area of Mexico City.
Pemex says its operations will continue to run normally – and commercial and financial obligations will continue to be met – despite the blast.
The company’s chief executive, Emilio Lozoya Austin, cut short a business trip to Asia and was on his way back to Mexico, a Pemex statement said.
At least 25 people were killed by a blast in Mexico City at the headquarters of the state oil company, Pemex
Relatives of employees have gathered outside the building in search of information about their loved ones, local media report. Some are said to have tried to reach employees on their mobile phones but have had no reply.
“The place shook, we lost power and suddenly there was debris everywhere. Colleagues were helping us out of the building,” eyewitness Cristian Obele said.
“We were talking and all of sudden we heard an explosion with white smoke and glass falling from the windows,” another witness said.
“People started running from the building covered in dust. A lot of pieces were flying.”
Images of the blast posted on Twitter revealed large clouds of smoke billowing from the building. TV footage showed people being transported from the scene by helicopters.
President Enrique Pena Nieto and Mexico City Mayor Miguel Angel Mancera headed to the scene of the blast.
Enrique Pena Nieto said Pemex rescue and security teams were working alongside city authorities to help the injured.
“I am deeply sorry for the deaths of our fellow workers at Pemex. My condolences to their relatives,” President Enrique Pena Nieto said on Twitter.
“At the moment, the priority is to help the injured and protect the physical safety of those who work there.”
The president said he has ordered an investigation into the causes of the blast.
Earlier on Thursday, Pemex had reported problems with the electricity in the building in a message on Twitter.
It later confirmed that an explosion had taken place “in the B2 building of the administrative centre”.
Plaster had fallen from the ceiling of the basement and the situation was “delicate”, a spokesman for local emergency services was quoted by the Reuters news agency as saying.
Pemex has experienced a number of fatal accidents in recent years.
Last September’s deadly blast at a gas plant near the northern town of Reynosa is thought to have been caused by a build-up of gas.
A large earthquake with a magnitude of 7.4 struck near Acapulco on Mexico’s Pacific coast on Tuesday, sending terrified workers and residents running into the streets and damaging an estimated 800 homes.
According to United States Geological Survey (USGS), the quake had a magnitude of 7.4 and put the epicentre at 15 miles (25 km) east of Ometepec, in Guerrero state.
Witnesses in the capital, Mexico City, said the tremor sent office workers rushing out onto the streets.
An estimated of 800 houses were damaged in Guerrero and Oaxaca states.
Guerrero’s governer Angel Aguirre told Milenio television that so far there were no casualties in Guerrero state or nearby Oaxaca state, adding that authorities were checking schools and public buildings near Ometepec.
The director of the country’s seismological service, Carlos Valdes Gonzalez, said that there had already been some six aftershocks and further ones could be expected in the next 24 hours.
Carlos Valdes Gonzalez said one of the aftershocks had already registered a magnitude of 5.3.
A large earthquake with a magnitude of 7.4 struck near Acapulco on Mexico's Pacific coast on Tuesday
A pedestrian bridge reportedly collapsed and crushed a microbus in Mexico City, but there were still no reports of deaths.
Office workers and residents were sent running into the streets in wealthy districts and poor neighborhoods alike.
Samantha Rodriguez, a 37-year old environmental consultant, was evacuated from the 11th floor of an office block.
“I thought it was going to pass rapidly but the walls began to thunder and we decided to get out,” she said.
Sirens could be heard across the city, and police helicopters are crisscrossing the skies.
“I swear I never felt one so strong, I thought the building was going to collapse,” said Sebastian Herrera, 42, a businessman from a neighborhood hit hard in Mexico’s devastating 1985 earthquake, which killed thousands.
Mexico City Mayor Marcelo Ebrard’s Twitter account said the water system and other “strategic services” were not experiencing problems and no damage was reported in the central or northern areas of the city.
Mobile phone networks have been affected, our correspondent says, and people have had trouble contacting their loved ones.
Gabino Cue, the governor of Oaxaca state, next to Guerrero state, said via Twitter that the quake had caused cracks in school buildings and damaged roofs in one part of the state.
The USGS said the epicentre was 11 miles (18 km) underground.
The US president’s daughter, 13-year-old Malia Obama, was on a school trip in Oaxaca, south-western Mexico. A White House official said she was safe and had never been in danger.