The Prime minister said plans were underway to send three ships – including the Ark Royal and HMS Ocean – on the rescue mission.
Meanwhile the Spanish government has agreed to provide a “hub” for Brits who can fly in and pick up alternative means of transport there.
UK flights will be grounded until at least 1am on Tuesday as the volcanic ash cloud continues to billow across Europe.
Brown also said he would review if anything could be done for airlines and other businesses losing millions in the crisis.
The Prime Minister said: "I believe this is one of the most serious transport disruptions we have faced.
"It's got financial consequences as well as human consequences and we will do everything in our power to make sure all the arrangements are in place to help people where possible to get back home."