A tropical depression in the Gulf of Mexico Thursday is threatening to grow into a storm that could further upend efforts to contain and clean up the massive BP oil spill.

Tropical storm warnings were issued for the coast of the southern US state of Texas and northeastern Mexico.

US meteorologists forecast the system will cut through the Gulf along a similar track as last week's Hurricane Alex and hit the US-Mexico coastline by late Thursday.

"Some slight strengthening is still possible and the depression could become a tropical storm before moving inland later today," the US National Hurricane Center reported.

The prospect of the second tropical depression of the Atlantic season strengthening into a major hurricane appeared remote, however.

"The depression has not become any better organized, and maximum winds remain near 35 miles (55 kilometers) per hour," the Miami-based NHC said.

Shortly before 0600 GMT the depression was about 340 kilometers southeast of Brownsville, Texas, and was churning to the northwest at 22 kilometers per hour.

While it is 800 kilometers from the site of the ruptured well that has been gushing millions of barrels of oil into the Gulf of Mexico, it can generate sufficiently large sea swells to hamper clean-up along the US Gulf Coast.

Hurrican Alex prompted a five-day shutdown in clean-up efforts from late June until last weekend.

High seas in the Gulf have scuppered immediate hopes of deploying a third ship that could help contain almost all the oil gushing from the blown out well on the sea floor off the coast of Louisiana.

Stormy weather has also delayed plans to deploy a Taiwanese mega-skimmer, A Whale, which could dramatically increase the amount of spilled crude that clean-up crews can scoop from the ocean surface.