AT THE SOUTH AFRICA-ZIMBABWE BORDER - For those desperate souls who would sneak across this frontier, consider the obstacles: Armed bandits. A river, low this time of year but still populated by crocodiles and man-mauling hippos. Multiple rows of fences watched by zealous border guards. And all along the goal is to enter a country that's dangerously hostile to immigrants.

Yet to escape President Robert Mugabe's Zimbabwe, the risks increasingly appear to be worth taking.

One of the largest illegal migrations in the world continues to swell as Zimbabweans stream into South Africa, fleeing a brutal crackdown by Mugabe in the run-up to last month's presidential election. Zimbabwe's main opposition party says that security forces and government militias have killed more than 100 of its members and abused or tortured thousands of others.

Three weeks after the election, which Mugabe won by default when his opponent withdrew because of the violence, hundreds of political activists remain in jail. Mugabe's militias haven't been disarmed.

A decadelong economic collapse already had emptied Zimbabwe of nearly a third of its people, but human rights groups say that the election attacks accelerated the flight into South Africa. Every week, soldiers and police arrest dozens, sometimes hundreds, of illegal migrants near the main border crossing outside the town of Musina. Authorities say that many more sneak across undetected.

The influx is putting more pressure on South Africa, the continent's most prosperous nation but one that views its estimated 5 million African immigrants -- who form more than one-tenth of the population -- with a volatile mixture of fear and resentment. In May, more than 60 were killed in an eruption of anti-immigrant violence across the country.

Most of the immigrants -- some say as many as 3 million -- come from Zimbabwe, the vast majority of them undocumented. In recent weeks, thousands have arrived in Johannesburg. Hungry and destitute, they're passing the coldest nights of the year in public parks, in the hallways of apartment buildings, on street corners and in churches.

"I'm very alarmed at the increase," said Paul Verryn, bishop of the Central Methodist Church in downtown Johannesburg, which has sheltered refugees for two decades. These days more than 2,000 Zimbabweans -- teachers, doctors, laborers, students, mothers and their infant children -- fill every room in the church, spilling into the stairwells and onto the pavement outside.

"The church has never received as many people as we are on a daily basis," Verryn said.

Among them is 29-year-old Tendai Mundoza, who jumped the border with her family last month after government militias beat her husband, an opposition supporter, outside their home.

"It's very difficult here," she said as her 10-month-old dozed on the thin cotton blanket that serves as the family bed. "It's too congested. The children become sick. But we can't go back home."

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