What started as a flight over New York City ended in the East River ... after a seaplane carrying eight passengers crashed Sunday afternoon, triggering a massive emergency response.

The aircraft made a hard landing in the River just after noon ... sending emergency crews racing to the scene, where witnesses watched as it partially capsized into the choppy water.

Waiting for your permission to load the Twitter Tweet.

Check out the dramatic video ... rescue boats quickly surrounded the plane as first responders rushed to pull everyone to safety. Officials say all 8 people aboard -- six passengers, a pilot and a crew member -- made it out alive, with no serious injuries.

Waiting for your permission to load TikTok Post.

After everyone was safely off the aircraft, crews righted the plane and towed it back to the dock as officials launched an investigation into what caused the rough landing.

At least five boats rushed to the scene ... while another seaplane circled nearby.

The scare comes less than a month after another seaplane ran into trouble in the East River during takeoff ... making this the second high-profile seaplane mishap in the same stretch of water in just a few weeks.

Sunday's flight didn't stick the landing ... but thankfully, everyone else did.