An attack that injured an as-yet unknown number of people in London Wednesday has caused San Francisco's airport to increase security, and has San Francisco police monitoring the overseas situation.

As reported by the BBC, the incident occurred at 14:40 GMT, which is 7:40 a.m. in San Francisco. Information on the attack is still being released, but according to the New York Times, police were called to London's Westminster Bridge on reports of “a firearms incident.” The Independent reports that an attacker "mowed down pedestrians on Westminster Bridge, before slamming his car into railings and stabbing a policeman outside Parliament." Gunfire was also reported outside the governmental building, the BBC reports.

"One police officer and at least two others" were killed in the melee, the Independent reports, with "at least" 20 more injured, even as other publications say the number killed and wounded is still unknown. The assailant, described as "middle-aged," was fatally shot by police, the Independent reports.

The San Francisco Police Department is monitoring news from London, spokesperson Officer Giselle Talkoff tells NBC Bay Area, "and will be ready to respond in the event that a local threat presents itself." Meanwhile, BART says that their "Critical Asset Protection team is on patrol as part of its regular schedule," and officials with the Golden Gate Bridge say that the agency is "always on high alert at the bridge to keep it safe from threats."

It's SFO that seems most concerned by the London attack, with "an increased amount of uniformed police officers" patrolling the terminals and tarmac, SFO spokesperson Doug Yakel tells NBC. All in all, Yakel says, "a heightened level of vigilance," is in place at the airport, but for now travelers should not expect protocols at the security check or gates to change.