Central America-4 Border Control Agreement
The Central America-4 (CA-4) Border Control Agreement was a treaty signed in June 2006 between the Central American nations of El Salvador, Guatemala, Honduras and Nicaragua, establishing the free movement across borders between the four signatory states of their citizens without any restrictions or checks. Foreign nationals who enter one of the signatory countries can also travel to other signatory states without having to obtain additional permits or to undergo checks at border checkpoints. Similar to the Schengen Agreement in Europe, the CA-4 Agreement establishes a harmonised visa regime for foreign nationals travelling to the area.
Foreign nationals eligible for visa-free entry 
Nationals of the below countries holding an ordinary, diplomatic, official or service passport do not require a visa in advance to travel to any CA-4 country for a maximum stay of 90 days:
As well as holders of official travel documents issued by the following organisations:
Tourist card 
The following foreign nationals holding ordinary, service, diplomatic or official passports are also exempt from the requirement to obtain a visa prior to arrival for a maximum stay of 90 days, though they are obliged to purchase a Tourist Card upon arrival to the CA-4 area for the countries that require it (USD10 in El Salvador, USD10 in Nicaragua):
In addition, Hong Kong Special Administrative Region passport holders are exempt from holding a visa when entering Nicaragua only for a maximum stay of 90 days, though a Tourist Card must be obtained at a cost of USD5.
Special exemption for diplomatic and service passport holders 
In addition, diplomatic and service passport holders from the following countries can enjoy visa-free travel to the CA-4 area:
See also 
- Visa regime information from the official website of the El Savador embassy in London
- Visa information for Hong Kong citizens