Passengers on a Hawaiian Airlines flight from Oakland to Honolulu were forced to evacuate the plane when it landed after the plane filled with smoke on its approach.

Hawaiian Airlines flight HA47 declared an emergency as it was on approach to Daniel K. Inouye International Airport in Honolulu. The flight, operated by an Airbus A321neo, landed at about 11:36 a.m. local time, according to data from FlightRadar24.

About 20 minutes before landing, the cabin, cargo hold, and cockpit began to fill with a heavy white smoke. The airline said in an emailed statement that the smoke was caused by a problem with one of the plane’s engine. Seven passengers were taken to the hospital for “smoke-related symptoms.”

“We have since determined that a seal failed in the aircraft’s left engine, causing oil to leak onto hot parts of the plane’s engine and air conditioning pressurization system, resulting in smoke in the cabin,” a spokesperson told the local news outlets KGMB and KHNL.

Read more: A Delta flight with nearly 200 people — including several celebrities — was delayed for 18 hours, leaving people sleeping on the airport floor

Emergency crews met the plane as soon as it landed, as passengers evacuated on the runway using the plane’s emergency slides.

“Scary last 20 minutes of our flight,” one passenger said in an Instagram post. “Mahalo Hawaiian Air getting us home safely.”

Passengers told Hawaii News Now that while the incident was scary, the evacuation was orderly, and flight attendants offered passengers wet cloths for people to breathe through.

Jon Snook, the chief operations officer at the airline, told the news outlet that a fire suppression substance was deployed in the cargo hold, although this was before the airline had determined the cause of the smoke condition.

The airline reportedly said that passengers on board the plane would get a full refund, along with a travel voucher.