Conception Casa, center, and his friend Jose Martinez, right, check on Rhonda Worthington after her car became stuck in rising floodwaters from Tropical Storm Harvey in Houston, Texas, Monday, Aug. 28, 2017. The two men were evacuating their home that had become flooded when they encountered Worthington's car floating off the road. (AP Photo/LM Otero) ORG XMIT: TXMO107

President Donald Trump has declared Sunday a national day of prayer for the victims of Harvey in Texas and Louisiana and the ongoing rescue and recovery efforts.

"The entire nation grieves with Texas and Louisiana," Trump wrote in a proclamation issued Friday. "We are deeply grateful for those performing acts of service, and we pray for healing and comfort for those in need."

Harvey made landfall in Texas as a Category 4 hurricane on Aug. 25. It stalled over the Texas Gulf Coast for several days, dumping massive amounts of rain onto Houston and the surrounding areas.

Though Louisiana wasn't hit as hard as some had expected, parts of southwest region of the state experienced severe flooding and tornadoes, prompting evacuations and causing some damage to homes. Five parishes have been issued federal disaster declarations, and the governor has asked that seven more be added to the list.

In the week since Harvey's landfall, Louisiana has sent teams of first responders and National Guardsmen to assist Texas. The state has opened seven shelters for Harvey evacuees -- most of them from Texas.

"People have never seen anything quite like this," Trump said in a proclamation-signing ceremony at the White House. "Individuals of every background are striving for the same goal: to aid and comfort people facing devastating losses. As Americans, we know that no challenge is too great for us to overcome -- no challenge."

Trump also dedicated his weekly address to Harvey. In it, he mentions working closely with Louisiana Gov. John Bel Edwards and Texas Gov. Greg Abbot. 

Trump and first lady Melania Trump are expected to travel to Louisiana on Saturday, as well as hard-hit Houston. 

Follow Elizabeth Crisp on Twitter, @elizabethcrisp.