TAPACHULA, Mexico (AP) — At least 1,300 mainly Cuban migrants fled on foot from an immigration detention center on Mexico's southern border Thursday in the largest mass escape in recent memory.

The National Immigration Institute said 700 of the Cubans had returned voluntarily, but 600 were still on the loose.

The institute said agents inside the compound weren't armed and "there was no confrontation."

Federal police with riot shields later streamed into the compound to control the situation, as a crowd of angry Cubans whose relatives were being held at the facility gathered outside.

The Cubans claimed their relatives reported overcrowding and unsanitary conditions at the facility.

"My wife and child have been in there for 27 days in bad conditions," said Usmoni Velazquez Vallejo, as he waited outside for news. "There is overcrowding, insufficient food and there isn't even medicine for them."

The escape was embarrassing for the government, given that the center's holding capacity had been listed at less than 1,000 people. The escape of 1,300 meant it was probably at least at double its capacity, since not everyone being held there escaped.

It was even more embarrassing coming on the same day Mexico's top human rights official toured the facility to oversee conditions there.