ARMENIA, Colombia (AP) _ Frustrated by a slow government food distribution effort, hundreds of hungry survivors of this week's earthquake looted a central market and a Red Cross relief center today.

Military police tried to halt the pillage with tear gas and live ammunition.

Photographers saw police fire over the heads of looters at the central market, where looters with cable-cutters, hammers and wooden clubs tried to break into shuttered stalls. At least two people were wounded, apparently by gunfire.

One of the looters, 45-year-old Heriberto Flores, passed out food and cleaning supplies to friends after being chased away by police.

``We're hungry. I lost two kids and I have two more at home who have to eat,'' he said.

Uptown, at the Red Cross center, scores of hungry homeless lost patience with eight-hour lines and bureaucracy and sacked the place. They had been waiting for their first rations and were forced to fill out forms and wait in two sets of lines.

Sixteen police officers stood by helplessly as people frantically grabbed plastic bags filled with rations, foam mattresses and plastic jugs of water, filling boxes and sacks with the goods. Some passed their plunder over a fence.

A television image showed one Red Cross worker seated on the warehouse's second-floor weeping, his head in his hands, as looting went on beneath him. Several blocks away, military police arrived and were arresting looters.

``The quicker we get organized the faster we will be able to work and distribute (the food), and the people themselves need to cooperate,'' President Andres Pastrana told reporters before returning to Bogota for an emergency Cabinet meeting.

Meanwhile, international rescue teams raced against time today, trying to find more survivors trapped under rubble four days after an earthquake leveled nearly half the city.

``We can't give up hope of finding people alive because nature determines the capacity for survival and it's very capricious,'' said Col. Hector Aguilar, head of a 120-man Mexican army rescue team, noting that babies were pulled breathing from the rubble 10 days after Mexico's devastating 1985 quake.

However, no one had been rescued alive in Armenia since Wednesday.

Some of the Mexicans pitched in to help Colombian rescuers reach the person they heard knocking under the rubble of a five-story apartment building Thursday.

``We knocked once and he knocked. Then we knocked twice and he knocked twice. Then we lost him and there was no more knocking. We don't know if he fell asleep or if he fainted or died,'' said Omar Tobon, an Armenia fire department official.

Pastrana sent 4,000 troops and imposed an overnight curfew in Armenia to crack down on looters who sacked dozens of markets and some homes after Monday's quake in western Colombia.

Until the frustration boiled over today, the street patrols had restored calm to most areas of Armenia and surrounding towns.

Rescuers from as far away as Japan and Russia, meanwhile, continued to remove bodies and heavy machinery chipped away at mounds of debris, many several stories high.

The magnitude-6 quake killed at least 940 people and injured 3,690, the Red Cross said. Many more were missing, and 200,000 were homeless.

A 3.9-magnitude aftershock was registered at 1 a.m. today, briefly causing panic in the streets, but no new damage or injuries were reported.

Air force planes delivered tons of water, food and medicine to the region, but a shortage of trucks and confusion among aid workers hampered delivery.

In Geneva, a spokeswoman for the U.N. World Food Program said it would begin distributing 200 tons of supplies today. The agency also is joining UNICEF on Monday in distributing high-protein biscuits and milk to children.

UNICEF estimates 100,000 of the 200,000 homeless survivors are children.

Not only the homeless found themselves utterly dependent on relief. The quake destroyed hundreds of stores, businesses and banks, leaving thousands whose homes remained intact without money or jobs.

``There's no money, there's no banks, there's nothing,'' said a despondent Olinda Otalva, who waited hours in a food line outside a market Thursday, only to find the supplies had run out.

Lacking running water or toilets, public health was also becoming a serious concern. Some residents bathed in the filthy streets, where thousands have camped out since the quake.

Doctors reported small outbreaks of diarrhea and gastroenteritis and were watching for respiratory infections in a city choked with dust and the growing stench of decay. Clinics offered free tetanus shots.

``It's not alarming yet, but it's beginning,'' said Jorge Raul Ossa, deputy director of medicine at Armenia's San Juan de Dios Hospital.

Thousands of people formed blocks-long lines to receive their first fresh food since Monday at markets and to get potable water from tank trucks.

At Armenia's downtown Cristal Supermarket, owner Jose Rubiel Mejilla Rios decided to give his food stocks away rather than risk the alternative.

``We either give it away or they take it away,'' Mejilla said.

Pastrana said 290 tons of humanitarian aid had been sent to the region but that 150 more tons of food were needed daily.

``The food we've gotten is minuscule,'' said John Mairo Cohecha, mayor of the neighboring town of Calarca.

Pastrana appealed for international help, including tents and tarps for the homeless, and residents whose homes survived were urged to take in refugees.