DUBAI, United Arab Emirates (AP) — A rescue helicopter crashed on Saturday near the world's longest zipline, killing its entire crew in Ras al-Khaimah in the northeastern region of the United Arab Emirates.

The National Search and Rescue Center said four crew members were onboard when the helicopter crashed.

The Civil Aviation Authority said the Agusta 139 helicopter crashed during a rescue mission at around 5:50 p.m. local time on Saturday near the UAE's highest mountain of Jebel Jais in Ras al-Khaimah.

Videos posted online by stunned onlookers show the helicopter diving into a tailspin before crashing and bursting into flames in the valley of a rocky mountain

Ras al-Khaimah's ruler Sheikh Saud bin Saqr Al Qasimi ordered an immediate investigation into the crash, which occurred near the site of the world's longest zip line measuring 2.83 kilometers (1.76 miles) long.

The zipline opened in February as part of an effort by the smaller, lesser-known emirate of Ras al-Khaimah to attract more tourists and residents from neighboring emirates like Abu Dhabi and Dubai.