Caracas, Venezuela ? Hundreds of thousands of whistle-blowing demonstrators demanding President Hugo Chavez’s resignation took to Venezuela’s streets Friday, the 19th day of a general strike that has crippled the oil-rich nation’s economy.

Strike leaders called Friday’s demonstrations, converging at the Plaza Venezuela in the heart of the capital, a “mega-march” and a “takeover of Caracas.”

The Chavez government has pledged to heed a Supreme Court ruling this week to return control of the Caracas police from the military to the mayor — a leading Chavez opponent.

Striking oil executives, on the other hand, have defied the Supreme Court’s order on Thursday to immediately return to work. Instead, they staged rallies at assembly halls across the country.

Across town from the anti-Chavez demonstration, about 10,000 Chavez supporters gathered for an impassioned rally.

“We cannot stay at home while the opposition is holding a march to overthrow Chavez,” said supporter Jesus Navarro.

The State Department issued a travel warning Friday urging U.S. citizens visiting Venezuela to leave and those intending to go to change their plans. The warning cited concerns over deterioration of the political and security situation.

Nonemergency employees of the U.S. Embassy and their families are also being asked to return immediately to the United States.

People line up in front of a gas station to purchase fuel in Caracas, Venezuela. The general strike aimed at forcing President Hugo Chavez to call early elections or resign has resulted in gasoline shortages throughout the country.

State television showed gasoline tanker trucks protected by soldiers entering Caracas, but most gas stations remained closed for lack of fuel, and the few still open had lines up to a mile long.

Juan Vaquero, president of the National Federation of Gasoline Retailers, said that more than 80 percent of Caracas’ gas stations were closed.

The general strike, begun Dec. 2 to force Chavez’s resignation or early elections, has reduced the oil output by the world’s fifth-largest exporter to less than 10 percent of normal and pumped up global oil prices.

The price of Organization of Petroleum Exporting Countries’ seven crude oils hit a two-year high of $29.56 a barrel because of the Venezuelan crisis.

General strike organizers say Chavez has wrecked the economy and polarized the nation.

Venezuela’s economy shrank 6 percent the first nine months of this year, unemployment is 17 percent and inflation is 30 percent.