Mexican President Enrique Pena Nieto's slim working majority in the lower house of Congress sat in the balance early on Monday after mid-term elections held amid widespread anger over corruption, gang violence and weak economic growth.

Early forecasts from Mexico's electoral authority INE showed his Institutional Revolutionary Party (PRI) and its partners winning between 246 and 263 of the 500 seats in the lower house. The PRI, the Green Party and the smaller New Alliance Party (PANAL) had a one-seat majority with 251 seats heading into the vote. The preliminary count suggested support for the PRI itself had waned somewhat since the presidential election in 2012.

In voting seen as a litmus test for the president, the PRI appeared to be losing in the key northern state of Nuevo Leon, where independent Jaime Rodriguez, known as "El Bronco," had at least a 6-point lead in exit polls conducted by the television network TV Azteca and other media.

The margin of error in the Azteca survey, however, was 3.8 percentage points. The ruling party candidate, Ivonne Alvarez, acknowledged the vote was close.

Rodriguez's popularity in a state that is home to the business hub of Monterrey was attributed to voters' disgust with all political parties, each with its own corruption scandals.

Midterm elections usually draw light turnout, but attention was unusually high this time as a loose coalition of radical teachers' unions and activists vowed to block the vote, and security forces were deployed to keep order.

Thousands of soldiers and federal police were deployed to guard polling stations where violence and calls for boycotts threatened to mar elections for 500 seats in the lower house of Congress, nine of 31 governorships and hundreds of mayors and local officials. The senate was not up for renewal.

National Electoral Institute reported that nearly 100 percent of polling places were able to open. The elections drew a turnout of between 47 and 48 percent, the electoral institute said.

The PRI lost seats, according to the official early count. But a surge in Green Party representatives, from 27 in the current congress to as many as 48, could give the PRI-Green coalition 251 of 500 votes, a majority the party has lacked until now.

Protesters burned ballot boxes in several states of southern Mexico in an attempt to disrupt elections, but officials said the vote was proceeding satisfactorily despite "isolated incidents."

"Considering the challenges we faced in this election, the balance has been positive," electoral institute head Lorenzo Cordova said in a national address after polls closed.

The deployment followed what has been described as the "dirtiest elections" in Mexico's democratic history. At least seven candidates and nine campaign officials have been murdered in the lead up to the vote. In one case, a note was left by the victim’s body promising the same fate for any other politician who didn’t fall in line with the drug cartel’s objectives.

Relatives and supporters of 43 students who went missing in Mexico’s Guerrero state last September organized a boycott of Sunday’s mid-term elections, with some burning election ballots in Tixtla — the city where the students attended the Ayotzinapa Normal School.

In Tixtla, activists approached voting stations where officials handed over materials for Sunday’s election, Sin Embargo, a Mexican news website, reported.

Protesters told polling officials that "tomorrow it may be their relatives who are forcibly disappeared," Sin Embargo added.

On Sept. 26, 2014, students from the Ayotzinapa Normal School — “normal” schools are free boarding schools that train the rural poor to become teachers, and are known for social activism — were organizing for an upcoming protest when local police opened fire on them in the city of Iguala.

In the aftermath, 43 students were missing, and are believed to have been handed over by the police to a local drug cartel and murdered. The students' relatives and classmates, however, reject the government's version of events and have vowed radical action until they are returned alive.

As activists burned the voting materials on Sunday, they shouted slogans including “Ayotzinapa lives” and “We will not allow the electoral farce,” Sin Embargo reported.

Parents of the missing students said they would go to all of the polling stations in Tixtla to try to prevent voting.

In bordering Oaxaca state, a section of Mexico’s teachers union, the National Coordinator of Educational Workers (CNTE), declared their own boycott of the mid-term elections.

Spokesman Mohamed Otaqui Toledo said the teachers’ action was because of “the simple fact that the political parties … are responsible for the approval of education reform,” TeleSur reported.

In Oaxaca's capital, masked protesters emptied a vehicle of ballots, boxes and voting tables and burned the material in the main square.

The state government reported 88 arrests related to the destruction of election materials and disturbances in the capital, Tuxtepec and Salina Cruz.

Thousands of teachers across Mexico have protested Pena Nieto’s 2014 education reforms — born from the president’s alterations to the constitution that called for all education to be privatized and for parents to pay students’ expenses.

The union is calling for the annulment of Articles 3 and 73 of the constitution, which was added for Pena Nieto's stated purpose of providing “quality education for all,” TeleSur reported. Article 3 calls for privatization of education and an end to free and mandatory schooling, while Article 73 says all financial costs should be covered by the parents of students, according to TeleSur.

Critics of the reforms said they would make education impossible for the poor to afford, and would transfer much of the teachers unions’ power to the federal government.

With wire services