(Reuters) - U.S. Border Patrol officials in southern California are sending agents and other resources to Texas to help stretched colleagues in the Rio Grande deal with a surge of immigrants illegally crossing the frontier, two Border Patrol union officials said on Friday.

Officials are trying to handle an influx of new arrivals, many of them unaccompanied minors from Central America, that has crowded facilities in Texas and led to efforts to move some to other states.

"U.S. Border Patrol San Diego Sector is sending Mobile Response Team trained agents from San Diego to enhance processing and detention capabilities in the Rio Grande Valley," said Gabe Pacheco, spokesman for the National Border Patrol Council Local 1613, which covers San Diego.

He said in a statement that additional resources would be deployed immediately to South Texas "to facilitate increased effectiveness."

A Border Patrol union official in the neighboring El Centro sector of southern California said it was also sending agents, and that the other resources included vehicles.

Plans to begin flying the immigrants to California from Texas for processing were abruptly called off last weekend without public explanation. Border Patrol union officials said that was due to public pressure.

More than 47,000 unaccompanied minors are thought to have entered the United States illegally between October and May, nearly twice as many as the previous year, many of them fleeing poor and violent countries such as El Salvador and Honduras.

President Barack Obama has called the flood of illegal immigrant children an urgent humanitarian crisis but has also warned parents not to send their children on the long journey, saying they would be sent back.

Shawn Moran, vice president of the Border Patrol Council, said about 100 Border Patrol agents have been sent to the Rio Grande from other sectors to help process new arrivals, and that another 150 volunteers were being sought.

The surge comes as a number of U.S. groups push for policy reform to let the roughly 11 million undocumented immigrants in the United States obtain a pathway to citizenship.

Many Republicans say the Obama administration is not doing enough to secure the southern border, and they blame the surge of children on the president's 2012 decision to give temporary relief from deportation to some young people brought to the United States illegally by their parents.

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