NATIONAL CITY (CNS) - A bogus bomb threat issued by a pair of would-be bank robbers -- one taking part in the crime via telephone -- forced the full evacuation and closure of a large South Bay strip mall for several hours Thursday.

The failed holdup attempt began about 9:15 a.m., when a tall, thin woman entered a Chase bank branch in the 1100 block of East Plaza Boulevard in National City, carrying two bags and wearing a hooded sweatshirt with the head covering pulled tight across her face, leaving only her eyes visible, according to police.

As alarmed employees watched, the woman put down the sacks -- one red and the other green -- on the floor of the lobby, Sgt. Mike Harlan said. Moments later, a man telephoned and told a worker the green bag contained a bomb that would be detonated unless the red one was filled with $100,000 in cash.

The masked woman then ran out of the bank, after which the bank workers made a 911 call and cleared everyone out of the office, Harlan said. Patrol officers arrived about two minutes later, surrounded the strip mall and evacuated the roughly two dozen businesses inside it, he said.

Police simultaneously searched the area for the robbers by ground and air.

A sheriff's bomb squad was sent in to determine if the bomb threat was valid, the sergeant said. The team sent in a robot with X-ray and video capabilities into the bank to look over the bags.

About 11:30 a.m., the explosives squad remotely detonated the sacks, determining that nothing hazardous had been inside them, police Sgt. Dennis Leach said. A short time later, authorities reopened the shopping center to workers and the public, he said.

Next to a free-standing kiosk near the bank, investigators found the female bandit's hooded jacket. A witness reported seeing her take the garment off and throw it to the ground while fleeing the area on foot to the west, Harlan said.