The Red Cross (IFRC) says that it can begin distributing crucial aid supplies to crisis-hit Venezuela in two weeks.
IFRC head Francesco Rocca said the group could initially help 650,000 suffering a lack of food and medicine.
The government has claimed the blackouts are the result of sabotage in an effort to force President Nicolás Maduro from office.
The power cuts have hit hospitals, public transport, water and other services, worsening a national economic crisis.
After Mr Maduro’s government allowed the Red Cross to help, opposition leader Juan Guaidó responded by saying it had “recognised its failure by accepting the existence of a complex humanitarian emergency”.
In February, Mr Maduro used the army to block an effort led by Mr Guaidó to bring in US-backed aid convoys.
Mr Guaidó, the head of the opposition-controlled National Assembly, declared himself interim president in January, winning the support of more than 50 countries, including the US.
Mr Maduro regarded the aid convoys as a veiled US invasion.
What has the Red Cross said?
Speaking at a news conference in Caracas, Mr Rocca said: “We estimate that in a period of approximately 15 days we will be ready to offer help. We hope to help 650,000 people at first.”
Mr Rocca said Venezuela had met the conditions for humanitarian work to be carried out.
Mr Rocca said the IFRC would need to be able to act with “impartiality, neutrality and independence” and no interference.
Mr Guaidó said on Twitter that the IFRC announcement was a “great victory in our struggle”.
Mr Maduro has yet to comment publicly on the move but, the BBC’s Will Grant says, is likely to paint it as the consequence of a Washington-backed economic war.
The US welcomed the announcement as a “real opportunity” and said it would be “happy to put some of our aid into this method of reaching the Venezuelan people”.
Hyperinflation and a lack of supplies has meant food and medicine are often unaffordable, leading to malnutrition.
How are Maduro and Guaidó in conflict?
They each claim to be the constitutional president of Venezuela.
Shortly after Mr Guaidó declared himself interim leader, his assets were frozen and the Supreme Court, dominated by government loyalists, placed a travel ban on him.
But the 35-year-old opposition leader defied that ban last month when he toured Latin American countries to garner support.
Mr Guaidó has continued to call for President Maduro to step aside and has urged the security forces, which have mainly been loyal to the government, to switch sides.