A ceasefire to end the 52-year-old war between the Colombian state and FARC fighters has gone into effect, with a full peace agreement expected to be signed in September.

The Revolutionary Armed Forces of Colombia, or FARC, has issued the order for its men to observe the ceasefire from midnight (05:00 GMT Monday).

Juan Manuel Santos, Colombia's president, said on Twitter: "This August 29 a new chapter begins for Colombia. We are putting down our weapons. We've ended the war with FARC."

Hundreds of thousands of Colombians have died since 1964 as government forces and FARC fighters battled in the jungles in what is considered Latin America's last major civil armed conflict.

Este 29 de agosto empieza una nueva historia para Colombia. Silenciamos los fusiles. ¡SE ACABÓ LA GUERRA CON LAS FARC! — Juan Manuel Santos (@JuanManSantos) August 29, 2016

On the government side, Santos on Thursday ordered the Colombian national armed forces to halt military operations against the FARC.

"The end of the conflict has arrived," he said on Twitter.

In a declaration before the media on Sunday in Cuba, where peace talks were held, Timoleon Jimenez, the FARC leader, said: "I order all our commanders and units and each one of our combatants to definitively cease fire and hostilities against the Colombian state from midnight tonight.

"We noted with excitement the president's order to the army. Consequently we are proceeding to give the same order to our troops."

READ MORE: Colombia - Talking peace with a FARC commander

The FARC declared a unilateral ceasefire in July 2015. But Sunday night's ceasefire is the first in which both sides have committed to a definitive end to the fighting.

"The ceasefire is really one more seal on the end of the conflict. It is the test of fire," said Carlos Alfonso Velazquez, a security expert at the University of La Sabana.

Al Jazeera’s Alessandro Rampietti, reporting from Bogota, said that the two sides are due to sign a full peace agreement at a formal ceremony some time between September 20 and 26.

"The Colombians will have the last word on the peace deal through a referendum on October 2," he said.

The ceasefire and definitive end of hostilities will be followed by a six-month demobilisation process.

From Monday, the FARC's estimated 7,500 fighters will start heading to collection points to give up their weapons under UN supervision.

Guerrillas who refuse to demobilise and disarm "will be pursued with all the strength of the state forces," Santos told El Espectador newspaper.

Before the demobilisation, the FARC will convene its leaders and troops one last time before transforming into "a legal political movement", according to a statement published on Saturday.

Peace referendum

On October 2, Colombians will go to the polls to cast ballots in a referendum that Santos hopes will endorse the peace agreement.

"A victory for the 'Yes' vote will be a mandate from citizens for future governments," Santos was quoting as saying by El Espectador.

"The plebiscite will grant the political legitimacy that is needed."

He said the exact question that will be posed to voters in the referendum would be announced "in the coming days."

READ MORE: Colombia and FARC rebels reach historic peace deal

"We are on the verge of perhaps the most important political decision of our lives," Santos said in a speech on Saturday

The territorial and ideological conflict has drawn in various left- and right-wing armed groups and gangs.

It has left some 260,000 dead, 45,000 missing and 6.9 million people uprooted from their homes.

Efforts to launch peace talks with a smaller rebel group, the National Liberation Army, have yet to bear fruit.

But with the country's biggest rebel group, the FARC, ordering a definitive ceasefire, the conflict appears to be reaching an end.