Brownsville Independent School District officer Raymond Hernandez helps evacuees to a shelter at Porter High School on Wednesday in Brownsville, Texas. (Dave Einsel/Getty Images)

Tropical Storm Dolly was downgraded from hurricane status late Wednesday, as forecasters predicted it would weaken further as it travels inland over Texas through the night.

Earlier in the afternoon, Dolly was downgraded to a Category 1 storm as it hit the Texas coast, making landfall on South Padre Island, just north of the Mexican border.

One is the weakest ranking on the five-level hurricane scale, with maximum sustained winds of 150 km/h, according to the U.S. National Hurricane Center. Landfall is when a storm's centre crosses the coastline.

At 11 p.m. ET Wednesday, the storm's centre was about 80 kilometres northwest of Brownsville and moving northwest at about 13 km/h.

Officials in low-lying Texas counties had feared the storm would bring torrential rains that could overcome levees holding back the Rio Grande River and cause widespread flooding.

"The levees are holding up just fine," said Cameron County Emergency Management Co-ordinator Johnny Cavazos. "There is no indication right now that they are going to crest."

On South Padre Island, a 17-year-old boy injured his head, broke a hip and fractured a leg when he fell from a seventh-floor balcony. Elsewhere, the roof of an apartment complex partially collapsed, although residents said no one was injured.

Deserted streets being patrolled

Across the border from Brownsville, in the Mexican city of Matamoros, police and military vehicles patrolled mostly deserted streets.

About 23,000 people were forced to leave their homes, though some were reluctant due to fears of looting.

"I didn't want to leave because I have been living in the same place for 40 years and I know what this is about," said Arturo Gutierrez, 55, a fisherman from the village of Chichonal who finally agreed to leave. "I am now going to the shelter because my wife forced me to."

The 2008 Atlantic hurricane season is a month ahead of schedule. On average, the fourth tropical storm does not occur until Aug. 29, but Dolly, which formed on July 20, was this year's fourth.

The past two Atlantic hurricane seasons left the United States largely unscathed after a series of powerful hurricanes in previous years, including Hurricane Katrina in 2005.

With files from the Associated Press