LISBON (Reuters) - A medical helicopter crashed in a mountainous area near Porto, Portugal’s second biggest city, killing two pilots, a doctor and a nurse on board, the country’s INEM emergency service said on Sunday.

A rescue operation was launched late on Saturday when the helicopter went missing around 6:30 p.m. on Saturday after dropping off a 76-year-old patient suffering from cardiac problems at a hospital in Porto.

INEM said in a statement that the helicopter was located at 1:30 a.m., confirming the deaths.

“INEM deeply regrets what has happened, expressing sincere and heartfelt condolences to the families of the victims,” INEM said.

According to INEM, the helicopter was on its way back to its base in the district of Braganca when it crashed in bad weather.