Above normal monsoon rains and deadly flooding have hit Pakistan hard this year, killing hundreds of people so far and wreaking havoc particularly in the province of Balochistan.

The army has been involved in rescue and relief efforts there.

"A Pakistan army aviation helicopter which was on flood relief operations in Lasbela, Balochistan lost contact" with air traffic control, the military said in a statement.

It said six people were on board, including "Commander 12 Corps who was supervising flood relief operations in Balochistan" but did not give details on what may have happened to the helicopter.

The commander, Lt General Sarfraz Ali, is the top army official in the region and one of the most senior in the military.

A search operation was underway to track the helicopter that a local senior police official told AFP had been missing for at least six hours.

"Police, military and local rescue officials are searching for it," the police official, Pervaiz Umrani told AFP.

Prime minister Shehbaz Sharif, who was in the province earlier Monday to inspect rescue activities, has termed the incident "alarming".

"The entire nation prays to Allah Almighty for the safety, security and return of these sons of the country who came out to help the flood victims," Sharif tweeted.

Sharif earlier criticized provincial civilian officials over the lack of aid for people displaced by the floods.

The army is Pakistan's most powerful institution, and civilian administrations depend on it heavily on it during natural calamities such as floods and earthquakes.

The monsoon flooding, which began in mid-June, has killed at least 478 people so far, with at least 136 dead in Balochistan alone.

Balochistan is also rife with ethnic and sectarian violence, but so far no militant group has claimed responsibility for any attack on a helicopter in the region.