KATHMANDU - Searchers found both the cockpit voice recorder and flight data recorder on Monday from a passenger flight that crashed killing at least 68 people in Nepal's worst plane accident in 30 years, officials said.

The data on the recorders may help investigators determine what caused the Yeti Airlines ATR 72 aircraft, carrying 72 people, to crash in clear weather on Sunday just before landing in the tourist city of Pokhara.

Both recorders were in good shape and would be sent for analysis based on the recommendation of the manufacturer, Teknath Sitaula, an official at Kathmandu airport, told Reuters on Monday.

Under international aviation rules, the crash investigation agency of the country where the plane was designed and built, is automatically part of the investigation.

ATR is based in France and the plane's engines were manufactured in Canada, by Pratt & Whitney Canada.

Rescuers were battling cloudy weather and poor visibility on Monday as they scoured a river gorge for passengers who are unaccounted for, more than 24 hours after the crash. Sixty-eight bodies have been recovered.

Reuters footage from the crash site showed rescuers looking at the charred remains of the plane near the gorge.

The plane, on a scheduled flight from Kathmandu to Pokhara, gateway to the scenic Annapurna mountain range, was carrying 57 Nepalis, five Indians, four Russians, two South Koreans, and one person each from Argentina, Ireland, Australia and France.

Pokhara police official Ajay K.C. said the search-and-rescue operation, which stopped because of darkness on Sunday, had resumed.

"We will search for the remaining four that are still missing,” he told Reuters. "It is cloudy now... causing a problem in the search."

All the bodies had been sent to a hospital, he said. A spokesperson for Pokhara airport also said that the weather was hampering rescue efforts, but that clouds were expected to clear later in the day.

Minutes before the aircraft was to land on Sunday, the pilot asked for a change of runway, a spokesperson for Pokhara airport told Reuters on Monday.

"The permission was granted. "We don't ask (why), whenever a pilot asks we give permission to change approach," the spokesperson, Anup Joshi, said.

Sunday's crash underlined the need for the government to split up the Civil Aviation Authority of Nepal (CAAN), which both regulates airlines and manages airports, experts said.

"The government must immediately separate the regulatory body and service provider by splitting the Civil Aviation Authority of Nepal (CAAN) which is doing both works now," K.B. Limbu, an aviation expert and a retired pilot, told Reuters.

"This leads to a conflict of interests."

Asked for comment, Sitaula, the Kathmandu airport official, denied that there was any conflict of interest in the functioning of CAAN.

"The regulatory and service provider (airport management) officials are separate and there is no cross-movement between the two bodies operating under the same organisation," he said, referring to the CAAN.

There are nine domestic airlines in Nepal, including Yeti Airlines and its unit Tara Air. Yeti and Tara plane crashes have killed at least 165 people in Nepal since 2000 out of a total of 359, according to data from CAAN.

Another 75 people have died in helicopter crashes this century in Nepal, which is home to eight of the world's 14 highest mountains, including Everest, and where sudden weather changes can make for hazardous conditions.

Experts say air accidents are usually caused by a combination of factors, and investigations can take months or longer.

Anju Khatiwada, the co-pilot of Sunday's ill-fated aircraft lost her husband Dipak Pokhrel in a similar crash in 2006. Khatiwada's remains have not been identified but she is feared dead.

Nepal has declared a day of national mourning on Monday and set up a panel to investigate the disaster and suggest measures to avoid such incidents in future.

(Reporting by Gopal Sharma, writing by Shilpa Jamkhandikar; Editing by Gerry Doyle and Raju Gopalakrishnan)