Delegates at the United States New Zealand Partnership Forum meeting in Christchurch are understood to be safe, but that could not be officially confirmed.
A US delegation of 43 government, business and community leaders was attending the forum, which began yesterday and was due to end this evening.
A group of nine US congressmen had left the city before the earthquake struck, and were visiting Parliament this afternoon.
Foreign Minister Murray McCully was also in Parliament this afternoon.
The whereabouts of US Assistant Secretary of State Kurt Campbell could not be confirmed.