California authorities are asking the public for help in locating a group of three bank robbers nicknamed the "High Jumper Bandits" because they jump on tellers' counters, point guns and take money.

The bandits have targeted a total of five banks in San Francisco and San Mateo counties since April, according to the FBI. In all the robberies, the suspects, covering their faces and bodies with thick jackets, gloves and other clothing to mask their identities, have held customers and employees against their will, according to the FBI.

The suspects have been described by witnesses as three black males between 20 and 35 years old.

The FBI declined to comment on how much money had been stolen over the course of the robberies, citing the ongoing investigation. The banks, which include branches of Wells Fargo, Metropolitan Bank and First Republic, also declined to provide that information.

The FBI said the most recent high jumper robbery took place on Aug. 1. Peter Lee, a public affairs specialist for the FBI, told ABC News that a customer was pistol-whipped during that robbery.

Witnesses noticed multiple handguns at the first robbery and one handgun at each of the subsequent robberies, said Lee.