The Spanish cabinet is to discuss the next steps in the process of King Juan Carlos’s abdication and the accession of his son, Crown Prince Felipe.
The king announced on Monday his intention to abdicate after nearly 40 years on the throne.
Ministers will discuss the steps needed to approve Crown Prince Felipe’s accession to the throne.
Juan Carlos was seen as popular for much of his reign, but recently many Spaniards have lost confidence in him.
Prime Minister Mariano Rajoy said the cabinet would consider “constitutional measures” needed to clear the way for the succession.
Spanish newspapers published special editions on Monday evening to react to the abdication
The Spanish constitution does not have a precise law regulating abdication and royal succession.
Mr Rajoy’s emergency cabinet meeting will draft an abdication law which must then be approved by parliament. Correspondents say that the process could take as long as a month.
The two main parties in parliament remain loyal to the monarchy.
But most left-wing parties are opposed and staged demonstrations attended by tens of thousands of people across many cities including Madrid and Barcelona.
“Send the Bourbons to the sharks!” protesters chanted in Madrid. The Spanish royal family is a branch of the House of Bourbon.
Many demonstrators are demanding a referendum on the future of the monarchy.
Spanish media say Prince Felipe will be proclaimed King Felipe VI by parliament on 6 June and a coronation ceremony will be held soon afterwards.
It is not clear when exactly that will be – King Juan Carlos was crowned five days after parliament proclaimed his as king.
The new king will inherit an institution that has been tarnished by scandals in recent years.