SINGAPORE - Plans to evacuate Singaporeans out of quake-hit Nepal have been delayed as three Republic of Singapore Air Force C-130 planes did not land at Kathmandu Airport on Monday.

Two of the RSAF planes were diverted to Calcutta in India. The third C-130, which left Singapore on Sunday night, was rerouted to the Indian city of Patna.

Defence Minister Ng Eng Hen said in a Facebook post on Monday that the diversions were due to congestion at Kathmandu's Tribhuvan International Airport.

"Ground commanders tell me that conditions at Kathmandu can be challenging. The airport is about 1,300m above sea level and weather conditions can change rapidly.

"Frustrating to all concerned, when so much help is needed," added Dr Ng.

The diversions have also put on hold the Republic's rescue and relief efforts. Onboard the planes are nearly 50 men and women from the Singapore Civil Defence Force's DART (including four dogs) and Changi Regional HADR Coordination Centre's advance team, as well as, relief aid.

Noting that other countries are also pledging assistance to quake-hit victims, Dr Ng said essential items like clean water, food, shelter and medical services will be needed in the short term.

Among the Singaporeans who were supposed to be flown out on Monday was Mr Smeumas Yeo, who is part of the Aluminaid Team Singapura 2015 team attempting to fly the Singapore flag on Mount Everest

The economics graduate got injured on April 15 during the team's Lobuche summit climb. He had surgery and was recovering at Norvic International Hospital in Kathmandu when the 7.8-magnitude quake shook Nepal.