Superstorm Sandy caused serious water damage to the UN Security Council chamber, forcing it to move to a temporary base for a special meeting on Wednesday, diplomats said.

The 15-nation council hurriedly called a meeting to pass an emergency resolution extending the mandate of the African-UN peacekeeping mission in Somalia for seven days.

The meeting should have been held earlier this week because the mandate was scheduled to end Wednesday. But it was called off because of the hurricane that hit New York on Monday.

The Security Council chamber is in the basement of the UN headquarters overlooking the East River, which spilled over into Manhattan during the storm.

There is "some water damage to the basement," said a UN spokesman, Farhan Haq, but the United Nations gave no other details and reporters were not allowed into the headquarters on Wednesday.

Diplomats, speaking on condition of anonymity, said the damage to the underground floors is understood to be "quite bad".

The UN headquarters has been closed since the storm but was expected to reopen on Thursday, a spokesman said.

The resolution on the Somalia peacekeeping force was passed in a hastily set up chamber in another part of the headquarters.

It noted "the exceptional circumstances in New York City arising from Hurricane Sandy" as the reason for just a seven-day extension to the mission, officially known as AMISOM.

Without the resolution, AMISOM, which is playing a key role propping up Somalia's fledgling government, would technically have become illegal from Thursday.