Canberra Raiders saw their NRL Finals hopes suffer a severe blow in controversial circumstances as they lost 28-24 to Cronulla Sharks.

The Raiders find themselves six points off a play-off place with six games to go after two key officiating decisions left Canberra coach Ricky Stuart to brand the 'bunker' video referee system a "waste of time".

Having reduced a 22-6 deficit to just four points, Canberra's defence stopped for an apparent knock-on, which was flagged by the linesman, to allow Sione Katoa to dot down for Cronulla, the bunker then ruling Jesse Ramien had not touched a Valentine Holmes pass.

A brilliant long pass to Brad Abbey at the other end from Joseph Leilua, whose two tries had put the Raiders back in the contest, was then ruled forward by referee Gerard Sutton, Canberra indignant as they were denied a fourth try. That eventually came through Jordan Rapana, but Canberra ran out of time to complete a comeback.

The NRL has since admitted the touch judge was wrong to put up his flag and Stuart said: "The bunker is a waste of time. For the referee to be able to use it as a tool for an 'I don't know' is wrong. The bunker is making it harder for the referees.

"When the forward pass was thrown by Leilua, all the Cronulla right-hand-side defence was offside, they were inside the 10 [metres]. Why weren't we given the penalty for being offside?"

Brisbane Broncos took full advantage of Canberra's contentious loss, running in eight tries in a 50-18 demolition of Finals contenders Penrith Panthers to strengthen their grip on the eighth and final play-off spot.

The Broncos saw a three-match winning run ended by New Zealand Warriors last time out, but were back to their best as they scored five tries in the first half, two coming from Tevita Pangai, while Jamayne Isaako, who signed a new four-year deal on Thursday, kicked 12 points in the opening 40 minutes.

Down 32-0 at half-time, Penrith improved after the break but Kodi Nikorima crossed for a second-half brace for Brisbane before Matthew Lodge rounded off the rout.