An LAPD station got firebombed by someone who threw a Molotov cocktail at its doors … but it was all captured on video, and cops already nabbed the suspect.

The frightening scene went down around 1 AM Sunday at LAPD’s Topanga Division Station and was caught on surveillance footage.

As you can see, the guy walks up with what appears to be an already-lit explosive device in his hand and hurls it at the front of the building, then takes off running.

Law enforcement sources tell TMZ … the Molotov cocktail cracked the station window but did not break it, and the explosion looked bigger on video than it actually was.

We’re told the suspect — later ID’d as Jonathon Rosin — was chased down by officers and arrested. He’s been booked for igniting an explosive, a felony, and is still in custody.