Aid groups and governments worldwide mobilized humanitarian efforts in the wake of the devastating 7.8-magnitude earthquake that rocked Nepal Saturday, killing thousands and leaving tens of thousands homeless. The United Nations said roughly 30 international medical and search-and-rescue teams have been dispatched to Nepal since the tremor that affected nearly the entire country. Online fundraising websites have begun pulling in hundreds of thousands of dollars for earthquake relief, and aid groups have indicated their plans to send emergency supplies and equipment to survivors. Among the countries contributing to the effort are Australia, China, India, New Zealand, Pakistan, the U.K. and the U.S., the BBC reported.

“Time is of the essence for the search and rescue operations,” Valerie Amos, coordinator for the U.N.’s emergency relief effort, said in a statement Sunday.

Groups such as the Red Cross, Mercy Corps, the United Nations Children's Fund (UNICEF) and the international charity Save the Children have offered resources to Nepal. “We’re just gearing up,” Roger Hodgson, deputy country director in Nepal for Save the Children, told the New York Times. Officials estimated 6 million people live in areas affected by the massive quake, and the long-term cost of rebuilding is estimated at $5 billion. “People have been resilient. But it’s been difficult to get people and supplies into the country, especially to rural areas far from Kathmandu,” Hodgson said.

The White House issued a statement pledging $1 million in disaster relief. A disaster response team was also dispatched. The British government said it had made $7.5 million available to charities working in Nepal. Norway pledged $4 million, the Times said.

UNICEF, headquartered in New York, said it plans to focus its immediate efforts on “life-saving interventions” -- essential medicines, food, drinking water and hygiene supplies. “UNICEF will conduct a rapid assessment of damages and needs within the coming hours, as conditions allow more access to the hardest hit regions,” the organization said in a statement Saturday. “UNICEF is ready to spearhead the response for children and has prepositioned supplies, including water purification tablets, hygiene kits, tarpaulins and nutrition supplies.”

Individual donors have raised more than $286,000 so far through Crowdrise, a for-profit fundraising website.

The earthquake’s death toll spiked to more than 4,000 Monday and was expected to continue to rise as rescue workers comb through the rubble in the Nepalese capital of Kathmandu, where the quake caused buildings to topple. Officials said they expected more people to be trapped in the remote mountain villages near the epicenter of the earthquake. Some communities were thought to have been buried totally in landslides.

Eighteen people were killed on Mount Everest, earth’s tallest peak, in an avalanche. At least 200 climbers were rescued from the mountain.