LOS ANGELES -- An Indiana man who said he was headed to a gay pride event in California had a loaded assault rifle with magazines rigged to allow 60 shots to be fired in quick succession, plus 15 pounds of chemicals mixed and ready to explode, authorities said.

James Wesley Howell, 20, also had two other loaded rifles, ammunition, a stun gun, a buck knife and a security badge when he was arrested in Santa Monica early Sunday, hours after an attack at a gay nightclub in Florida left 49 people dead, police said.

The timing led to increased security at the L.A. Pride event in West Hollywood, which attracts hundreds of thousands of people. Authorities have not disclosed evidence that Howell planned violence at the event.

Alone, each item found in the car might not indicate anything sinister, Los Angeles County Superior Court Judge Keith Schwartz said at Howell's first court appearance Tuesday. But together, they "just don't pass the common sense test."

"I cannot in good conscience think of any reasonable reason that somebody would be travelling across the country with all of these things," he said, setting bail at $2 million.

Howell pleaded not guilty to three felony weapons and ammunition charges. He has told police he recently drove from Indiana to Los Angeles because of pending charges against him in his home state.

Friends in Indiana described Howell as a gun enthusiast with a short temper. In October, he twice was accused of pulling a gun and making threats, once against his then-boyfriend and once against a neighbour.

Howell was convicted in April of misdemeanour intimidation for the incident with his neighbour. Under the terms of his probation, Howell was not allowed to have weapons or leave Indiana.

When he was picked up in Santa Monica, there was an assault rifle in his car's passenger seat and 15 pounds of "Shoc-Shot," two chemicals that explode when mixed and shot. The assault rifle was loaded with a 30-round magazine, which had another inverted 30-round magazine taped to it, police said.

Deputy District Attorney Sean Carney said gun enthusiasts don't mix Shoc-Shot until it's ready to be used, as federal regulations require, and the amount that Howell had "far exceeds any amount that would reasonably be used."

Howell's attorney, Pamela Jones, told the judge there was no evidence Howell planned to detonate the chemicals. She said a black hood found in his car was "just a clothing item," and nothing indicated Howell planned to use it as a mask, as police contended was a possibility.

James Wedick, a former longtime FBI agent, said the manipulation of the gun magazines would allow someone to reload 30 rounds in less than 2 seconds.

"It doubles your killing capacity by 100 per cent," he said. For a civilian to have a weapon rigged as such, "it suggests his purposes are deadly."

Federal agents searched Howell's home in Jeffersonville, Indiana, on Monday but declined to release any details.

Rebecca Lonergan, a former federal prosecutor who teaches national security law at the University of Southern California, said filing the state charges keeps Howell in custody while the FBI builds a possible case.

"In the atmosphere we have where there is such great concern about active shooters, about terrorism, about hate crimes, both the state and federal investigators are going to want to thoroughly look at this guy," she said.

The sheriff's office in Clark County, Indiana, said Tuesday that Howell also is the subject of a sexual assault investigation. The office says the incident occurred May 31.

Davies reported from Indianapolis. Associated Press writers Christopher Weber and Christine Armario in Los Angeles, Claire Galofaro in Jeffersonville, Indiana, and Dylan Lovan in Charlestown, Indiana, contributed to this report.