A US navy helicopter crashed near Tokyo Monday in a failed emergency landing, injuring two of the four men on board, rescuers said.

Television footage showed the grey helicopter on its side on what appeared to be vacant land, with mangled propellors and a snapped tail-end.

The accident came at a sensitive time, with the Japanese public wary over the long-planned but stalled relocation of a US base in southern Okinawa.

Around half of the 47,000 US service personnel in Japan are based on the strategically located island chain, which is nearer to Taiwan than it is to Tokyo.

Accidents, crime and noise associated with the bases make them locally unpopular, although Japanese people as a whole welcome the US defence umbrella they help to provide.

Monday's crash happened mid-afternoon in Miura city, roughly 60 kilometres (38 miles) south of Tokyo, said a local fire department spokesman.

One crew member told local authorities that the helicopter experienced a transmission problem, national broadcaster NHK said.

"One person broke a thigh. Another person suffered a contusion on his thigh. The remaining two apparently escaped any injury," he said.

The accident did not cause a fire and the rescue operation ended quickly with the injured men taken to a local civilian hospital in neighbouring Yokosuka, home to a major US naval base.

The US navy in Japan said it could not comment on the issue immediately.

A 2004 incident in which a helicopter crashed into a university building in Okinawa sparked widespread outrage and fuelled anti-base animosity.

The accident was key in the 2006 decision to move an airbase in a crowded urban area of Okinawa to a quiet stretch of seashore.

However, the move has been stalled because of objections from the new host community.