Indonesia has formally asked the United States for help in locating the AirAsia jet carrying 162 people that went missing on Sunday, the US State Department said on Monday.

"Today we received a request for assistance locating the airplane, and we are reviewing that request to find out how best we can meet Indonesia's request for assistance," State Department spokesman Jeff Rathke told a regular news briefing.

The US Defense Department said the details of the request were still being coordinated but "could include some air, surface and sub-surface detection capabilities."

"We stand ready to assist in any way possible," Pentagon spokesman Mark Wright said in a statement.

Rathke said the Indonesian request was made via a diplomatic note to the US Embassy in Jakarta. He declined to give details of the request.

"Our embassy, of course, is focused on finding ... ways to be responsive. Of course, we've been in close contact with Indonesian officials since the disappearance of the plane," Rathke added.

The Indonesia AirAsia plane, an Airbus A320-200, disappeared after its pilot failed to get permission to fly higher to avoid bad weather during a flight from the Indonesian city of Surabaya to Singapore on Sunday.

The head of Indonesia's search and rescue agency said earlier on Monday the missing jet could be at the bottom of the sea after it was presumed to have crashed off the Indonesian coast.