BATON ROUGE • After a much-criticised delay, US President Barack Obama visited flood-stricken Louisiana, defending his administration's response and urging citizens to pitch in and help ravaged communities.

He touched down in Baton Rouge on Tuesday and toured a hard-hit and debris-strewn parish, promising Louisianans they would get all the help they need. At least 13 people have died and more than 100,000 people have registered for emergency assistance as a result of the flooding.

The National Guard has been deployed and the federal government has approved over US$120 million (S$162 million) to assist with things like temporary rent, home repairs and flood insurance payments.

"I am asking every American to do what you can to help get families and local businesses back on their feet," Mr Obama said, directing people to the website volunteerlouisiana.gov and relief groups.

Mr Obama has been lampooned for not cutting short a two-week vacation in Martha's Vineyard to visit the Gulf Coast state. Heavy rains began on Aug 11 and quickly submerged thousands of homes.

In just a few days, almost 80cm of rain fell on some parts of the low-lying state - where the highest point is just 165m above sea level.

Republican presidential nominee Donald Trump visited Louisiana last week, and goaded the golf-loving President about his absence.

"Honestly, Obama ought to get off the golf course and get down there," he said.

Mr Obama dismissed such criticism, saying: "This is not a photo-op issue...This is (about) how do you make sure that a month from now, three months from now, six months from now, people still are getting the help that they need."

AGENCE FRANCE-PRESSE