CAIRO — Thousands of antigovernment protesters in Bahrain blocked access to the financial district in Manama, the capital, on Sunday, preventing workers from getting to their offices and pushing back police officers who tried to disperse them.

It was the most serious challenge to the royal family that rules Bahrain since protests began last month.

Witnesses said the police used tear gas and fired on the protesters with rubber bullets.

“This was a very, very big day,” Mohammed al-Maskati, president of the Bahrain Youth Society for Human Rights, said by telephone from Pearl Square, the epicenter for protests in central Manama. “Now the protesters control these streets. There are walls of rubble keeping out the police and armed groups. People say they will not sleep tonight.”

There were also clashes at the campus of the main university, where protesters contended that the security forces were protecting armed vigilantes accused of fomenting tensions between the 70 percent of the population that is Shiite Muslim and the Sunni ruling family and elite.