LONDON (Reuters) - A magnitude 6.0 earthquake struck in the Gulf of California off the Mexican coast early on Monday, the U.S. Geological Survey said, with initial reports suggesting it caused no casualties or significant damage.

The quake was centered 57 miles southwest of Los Mochis in Sinaloa, Mexico, at a depth of 6.3 miles, USGS estimates showed.

According to Mexico's national seismology institute, the quake measured 5.7 and was centered 99 kilometers (62 miles) southwest of Ahome, Sinaloa. It struck at 1.26 a.m. EDT.

"We felt a tremor, the building shock and we went outside, that was all," said a local police officer in Los Mochis. "There is no damage to buildings and everything is normal." He knew of no injuries.

"We felt it hard, and it shook the building like we've never felt before," said Rafael Ines, an editor at Los Mochis paper El Debate. "It was a pretty hardcore shake."

(Reporting by Gabriel Stargardter; Editing by John Stonestreet)