Republicans in the United States House of Representatives have voted to crack down on Central American migrants, including unaccompanied children, who are flooding to the border with Mexico.

The child migrant crisis has become an increasingly hot topic ahead of the mid-term elections in November that will determine control of US Congress next year.

The vote came as lawmakers passed a $US694 million border security bill, one day after conservative Republicans balked at an earlier version of the measure, exposing a deep rift between Tea Party activists and more mainstream Republicans.

The Republicans have been trying to present a united front against president Barack Obama to energise the party's voting base, including a move this week to sue him in federal court for allegedly overstepping his legal authority.

In passing the retooled bill, the Republican-led House ignored a veto threat from the White House, but with the Senate already on a five-week summer recess, the measure will advance no further until at least September.

"We couldn't go home [for recess] and not have a decision," said Kay Granger of Texas, who helped draft the original bill.

Ms Granger said the measure would serve as a marker for negotiations in September to resolve the humanitarian crisis that has seen nearly 60,000 children from El Salvador, Honduras and Guatemala arrive illegally since October to escape criminal drug gangs and poverty.

House Democrats complained that the legislation would too speedily return children to dangerous conditions in their home countries.

Mr Obama called the Republican bill "extreme" and "unworkable".

Later the House passed a separate Republican bill to reverse Mr Obama's policy of suspending deportations of undocumented residents who were brought to the US illegally by their parents when they were children.

The House also passed a bill that also would stop Mr Obama from expanding his policy to other groups of undocumented immigrants.

The bill would also prohibit those who have already been given a reprieve from deportation from renewing their status when it expires after two years.

The Democrat-controlled Senate is not expected to consider the House bill.

With Mr Obama's $US3.7 billion border funding request rejected by Congress without alternative legislation presented to him for signing into law, he said he would shift funds from other accounts to pay for enhanced border security and the care and feeding of thousands of detained migrant children.

"I'm going to have to act alone because we don't have enough resources," Mr Obama said.

"We've already been very clear. We've run out of money."

The tougher language in the twin bills would also make it easier to deport migrant children and add money to deploy National Guard troops at the border with Mexico.

The Republican push could aggravate immigrant communities that have been hoping for comprehensive reforms.

Reuters