Five illegal immigrants died after crossing the border into southern Arizona's treacherous desert and authorities searched Monday for a sixth.

"We're hoping to find him or her alive," said Andy Adame, a spokesman for the Border Patrol's Tucson Sector (search), which covers most of the Arizona-Mexico border.

Four survived. They and the other six had become stranded in rugged terrain Sunday after crossing the border.

Temperatures soared over 100 degrees Sunday.

One of the survivors was a Mexican man who sought help Sunday morning at a ranch west of Gila Bend, about 75 miles north of the border, Adame said.

Over the next several hours, Border Patrol search crews found four dead migrants and a fifth who died while en route to a hospital.

More than 90 illegal immigrants (search) have been found dead since Oct. 1 in the Arizona desert, the busiest illegal entry point along the U.S.-Mexico border.

"It surprises me that we have not had more deaths in large groups," said the Rev. Robin Hoover, founder of Humane Borders (search), a group that puts water in the desert for illegal crossers.

A record 154 immigrants died in Arizona in the 2003 fiscal year that ended Sept. 30, most of them succumbing to the desert heat. Similar numbers have been recorded in recent years.

The single-deadliest border crossing in Arizona history occurred in May 2001, when Border Patrol agents found 14 dead immigrants on the Cabeza Prieta National Wildlife Refuge (search) near Yuma. Twelve others survived, including a smuggler.

Adame said he didn't know how long the group found Sunday had been in the desert. He also didn't know their nationalities, except for the man who went for help.

Three of the immigrants were hospitalized and were expected to survive, said Adame. One of them, a woman, was taken to a Phoenix hospital, where she was reported in stable condition. Officials wouldn't release further details Monday. It was unclear where the others were taken.

The man who reported the group was treated for dehydration and didn't require hospitalization. He was in Border Patrol custody Monday, along with one of one of the three other survivors, who had been released from the hospital, Adame said.