The declaration was necessary "due to the unprecedented and extraordinary amount of foreign inference in the December 1 presidential elections and also in the internal affairs of The Gambia," Jammeh said on state television.
Gambian President Yahya Jammeh on Tuesday declared a state of emergency just two days before he is due to step down, citing "extraordinary" foreign interference in the country's post-electoral crisis.
The declaration was necessary, he said on state television, after the "unprecedented and extraordinary amount of foreign interference in the December 1 presidential elections and also in the internal affairs of The Gambia."
The 15-nation Economic Community Of West African States (ECOWAS) has repeatedly called on Jammeh to respect the result of the vote he lost to opponent Adama Barrow and step aside, backed up by the United Nations Security Council, African Union and several other institutions.
Jammeh said foreign powers had created an "unwarranted hostile atmosphere, threatening the sovereignty, peace, security and stability of the country," forcing him to act.
Under the Gambian constitution a state of emergency lasts seven days if the president declares it unilaterally but up to 90 days if the national assembly confirms it, which has not yet happened.
The terms of the declaration were left vague by Jammeh and seemed to correspond to laws already in place in a nation where human rights abuses are rife.
All citizens and residents were "banned from any acts of disobedience to the laws of The Gambia, incitement to violence and acts intended to disturb public order and peace," Jammeh said.
He then asked the security forces to maintain law and order.
The move will be dimly viewed by the international community as Jammeh's mandate runs out, but the president has shown little interest in diplomacy after rebuffing two high-level delegations by west African leaders in recent weeks pleading with him to go.
Meanwhile four more cabinet ministers in Jammeh's government defected, a source close to the regime told AFP on Tuesday, while citizens stream out of the country in fear of unrest.
Foreign minister Neneh Macdouall-Gaye, finance minister Abdou Kolley, trade minister Abdou Jobe and tourism minister Benjamin Roberts had all resigned, the source said, requesting anonymity for safety reasons.
Roberts was appointed to replace Kolley on Monday, meaning he spent less than 24 hours in the new post, local media said.
The latest resignations came after the high-profile defection last week of information minister Sheriff Bojang, who is now sheltering in neighbouring Senegal.
Citizens continued to pack their bags and stream out of Banjul by road and ferry for Senegal, Guinea-Bissau and Guinea, taking as many possessions as they could carry.
One traveller told AFP that those arriving at 10:00 am would have to wait until the following day to board a ferry at Banjul port to cross the river headed for Senegal, unless they bribed officials, due to huge numbers exiting the city.
The UN's refugee agency has said several thousand Gambians have crossed the border in the last few weeks to shelter with extended family while they await January 19, when Jammeh is due to hand over power.
Barrow is in Senegal, where he plans to remain until his planned inauguration on Thursday.
The spectre of a military intervention in The Gambia now seems closer than ever, following declarations by the United Nations and African Union that boots on the ground could get the green light without a rapid resolution to the crisis.
Fears of conflict were ramped up in Banjul following the weekend arrest of soldiers suspected of being sympathetic to Barrow, underlining significant disagreement within the armed forces over whom they will support come Thursday.
Elsewhere Liberian President Ellen Johnson Sirleaf hit out at Jammeh for broadcasting a conversation they held by phone on Sunday on Gambian television without her knowledge.
"Unfortunately, being the person that he is, Jammeh recorded and televised their conversation without advising her of his intent to do so," a statement from the Liberian presidency said.
Sirleaf was then quoted as saying that as of Monday "there is no change in ECOWAS position. The Constitution of The Gambia must be respected."
In Rabat, it was reported that Morocco had offered Jammeh asylum for accepting the election defeat and stepping down "in return for a golden retirement", but Banjul sources were reluctant to confirm the claim.
And in a growing sign of Jammeh's hostility to international scrutiny, seven journalists from China, Sweden and Senegal were expelled late Monday soon after they arrived at Banjul airport to cover the ongoing crisis.