The incident took place at around 3.06 PM (local time) yesterday when an "adult male subject, carrying a firearm, approached an outer perimeter checkpoint accessible to the general public" on E Street near the White House, the Secret Service said.
The Secret Service agents on duty gave numerous verbal commands for the accused to stop and drop the firearm.
"The Secret Service recovered a firearm at the scene," he said.
The man has been admitted to a nearby hospital with critical injuries, officials said.
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As a precautionary measure following the incident, the White House was immediately put under lockdown, with doors locked and agents in full tactical gear and armed with automatic and heavy-caliber weapons deployed around the complex and Lafayette Square to the north.
President Barack Obama was not present on the premises at the time of the incident as he had gone to play golf at Andrews Airforce Base.
Vice President Joe Biden was in the complex and the Secret Service agents rushed to him for additional security.
During a search of the man's vehicle parked near 17th Street and Constitution Avenue, federal agents found ammunition for a .22 caliber weapon.
Based on preliminary investigation, the Federal Bureau of Investigation and other law enforcement agencies said the shooting incident has no known nexus to terrorism.
"However, an investigation continues into the motives behind his actions. The investigation is ongoing, and will continue to follow all logical leads," said the statement issued late in the night.