Ghost towns are nothing new in Mexico. Entire villages have long been left empty, as residents with no way to make a living migrate to the US for jobs.

But now a force beyond mere economics is causing Mexicans to shutter their windows and flee: drug violence.

In the state of Michoacan, residents in villages throughout the “Tierra Caliente” or “Hot land,” where drug traffickers who rule swaths of territory have fled their homes to take refuge in impromptu shelters after gun battles between rival drug gangs erupted this week.

“All of the residents of little towns have fled,” says Hugo Rodriguez, who works in the human rights office in Apatzingan, the principal city in this region of Michoacan. “For their own safety, they took their families and temporarily moved into shelters.”

An official in the state told the Associated Press that some 700 had left their homes and slept at a water park in Buenavista Tomatlan this week. Others have moved temporarily into community centers and churches. Local media has reported that up to 2,500 people have fled the various towns in this part of the state in recent days.

This mass evacuation comes after one in November, in which hundreds of residents in Ciudad Mier, in northern Mexico, fled for a neighboring town, after the drug group the Zetas issued a letter saying that if any residents remained they would be killed. Some 400 left and have since returned home.

Mexico’s drug violence is often compared with that of Colombia, but the four-decade-long battle between leftist guerrillas and the state and more recently with drug traffickers has caused far more displacement, with over three million internally displaced people. Just this week the Colombian Congress paved the way for the return of millions of acres of land and reparations for the displaced (see yesterday's blog post).

In Mexico, some 230,000 people have been forced to flee their homes, according to the Internal Displacement Monitoring Center (IDMC), based in Norway.

Most have left northern Mexico, especially in towns like Ciudad Juarez that have been in the crossfire of drug violence. That city's Municipal Planning Institute has reported that in 2010 up to 116,000 homes were vacant. According to the IDMC, using survey data from Ciudad Juarez, in 2010 alone some 230,000 fled their homes.

About half went north to the US, leaving some 115,000 internally displaced people in Mexico.

The number of those leaving smaller towns, where security is scant, has not been quantified, but is growing. It is hard to distinguish between those fleeing because of violence and for economic reasons, and many times the evacuation is temporary.

Mr. Rodriguez, for example, says that many of the displaced in Michoacan are already planning to return home as the situation calms down. But, here's some perspective: During the 1990s some 60,000 people were displaced from Chiapas, according to the IDMC, in the wake of the Zapatista Army of National Liberation uprising. That's a quarter of those forced to flee today.

It will not be surprising if more towns empty out in the face of drug violence, which has spread throughout the country.

This week in the state of Nayarit, in western Mexico, a gun battle between two rival gangs left 29 dead. And in another ongoing case, the man who allegedly ordered the killing of the son of the poet Javier Sicilia, who has been leading peace marches across the country, has been arrested.