Doug LaMalfa, a Republican Congressman from California, has died unexpectedly at age 65, colleagues announced on Tuesday.

President Donald Trump offered a tribute to LaMalfa, saying he wanted "to express our tremendous sorrow at the loss of a great member - a great, great, great member".

The congressman's cause of death was not immediately clear. LaMalfa was a former rice farmer elected to congress in 2013. He focused on water and agriculture issues during his tenure.

His death shaved an already-thin Republican majority in the US House of Representatives to just a few seats, following the resignation on Monday of former Trump ally Marjorie Taylor Greene.

"He was a fantastic person," Trump said. "He voted with me 100% of the time."