(Adds arrival at Chula Vista station in paragraphs 13-14)
By Marty Graham
MURRIETA, Calif., July 2 (Reuters) - Protesters shouting anti-immigration slogans blocked the arrival of three buses carrying undocumented Central American families to a U.S. Border Patrol station on Tuesday after they were flown to San Diego from Texas.
The migrants, a group of around 140 adults and children, were sent to California to be assigned case numbers and undergo background checks before most were likely to be released under limited supervision to await deportation proceedings, U.S. immigration officials said.
But plans to bring the immigrants to a Border Patrol outpost in Murrieta, 60 miles (100 km) north of San Diego, sparked an outcry from town mayor Alan Long, who said the migrants posed a public safety threat to his community.
The group is part of a growing wave of families and unaccompanied minors fleeing Guatemala, El Salvador and Honduras and streaming by the thousands into the United States by way of human trafficking networks through Mexico.
Most have shown up in Texas, overwhelming detention and processing facilities there.
The surge has left U.S. immigration officials scrambling to handle mass numbers of Central American migrants who, by law, the government cannot immediately deport, as they normally could illegal border crossers of Mexican or Canadian origin.
More than 52,000 unaccompanied children from Central America have been caught trying to sneak over the U.S.-Mexico border since October, double the number from the same period the year before, according to U.S. Customs and Border Protection figures. Thousands more were apprehended with their parents.
The group caught up in Tuesday's confrontation arrived by plane at midday in San Diego from Texas, where they had been apprehended while trying to cross the border, and were put on three unmarked buses for the ride to Murrieta.
As the buses neared their destination, some 150 protesters waiving American flags and shouting "Go home - we don't want you here," filled a street leading to the access road for the Border Patrol station, blocking the buses from reaching the facility.
The demonstrators disregarded orders from police to disperse, but officers did not attempt to intervene physically to break up the demonstration.
After about 25 minutes, the buses backed up, turned around and left. A board member of the union representing border patrol agents, Chris Harris, said the buses would likely be rerouted to one of six other Border Patrol stations in the San Diego sector.
Lois Haley, a spokesman for the Immigration and Customs Enforcement agency, declined to say where the buses were headed.
Local television station San Diego 6 said the buses went to the Chula Vista Station where about 140 migrants, mainly women and children, could be seen entering, though it was unclear if they were processed inside. It also said several of the children were taken to hospital for unspecified treatment.
A supervisor at Chula Vista declined to comment.
A separate group of undocumented families with children was being sent on Tuesday to a similar processing facility in El Centro, California, a desert community about 100 miles east of San Diego, U.S. immigration officials said. But there was no word on any disruptions of their arrival. (Reporting by Marty Graham and Eric M. Johnson; Writing by Steve Gorman; Editing by Alison Williams)