Thousands of South African university students protesting planned tuition hikes flocked to the country's main government complex on Friday, with some setting tires on fire and throwing stones as police responded with stun grenades and a water cannon.

One of the biggest student movements to have emerged since South Africa rejected white minority rule in 1994 poses a challenge to the ruling African National Congress party.

"We should be having free education," said 18-year-old Bongani Shabangu, who is studying education at a Pretoria university. "Most of us are from poor families."

Lucky Mahlatse, a 20-year-old computer science and statistics student, said more challenges lie ahead for graduating students.

"It's not that easy to get a job," he said.

Security forces periodically detonated stun grenades to clear students who were trying to force an opening in the fence and throwing stones at police officers. Most of the protesters were not involved in the clashes.

The students, some chanting and singing, had gathered in throngs on a large lawn at the foot of the Union Buildings in the capital, Pretoria, capping more than a week of protests against tuition increases planned for next year.

Many students accuse the government of not doing enough to support university students and their families who are struggling to pay bills.

President Jacob Zuma was scheduled to meet student leaders and university managers inside the Union Buildings on Friday. He and other leaders of the ruling party have said they are sympathetic to student concerns and welcome their protests, as long as they are peaceful.

A police helicopter flew overhead as some students pushed and pulled on a fence preventing them from getting closer to the government offices.

"Stop corruption, fund students," read one student placard. Another said: "Dear Mr. President: How do you sleep while the rest of us cry?"

Costs vary, but annual tuition for undergraduate students in South Africa runs to several thousand dollars at some universities. That amount, combined with textbook and accommodation costs, is a burden for many poor students in a country with a wide gulf between the affluent and those with limited means.

The protests began last week at the University of the Witwatersrand in Johannesburg, which later dropped plans for a 10.5 percent tuition hike in 2016 and has suspended classes until at least next week because of the disruption.

Many universities are in exam season, and there have been reports of protesters going into lecture halls and forcing some students to stop taking exams. On Wednesday, a student protest outside parliament in Cape Town turned violent and 30 demonstrators were arrested.