A Sydney bus driver has been charged with using a mobile phone while behind the wheel after a crash that left two people dead.

Two men, aged 32 and 28, died when their motor scooter was hit by a bus in the south Sydney suburb of Kingsgrove last night.

The 49-year-old bus driver, Luis Rajos, was charged with two counts of dangerous driving occasioning death, negligent driving occasioning death, using a mobile phone when not permitted and not wearing a seatbelt.

Luis Rojas appeared in Sutherland Court where he was denied bail. ( Supplied: Vincent de Gouw )

He was refused bail by a Sydney judge who said he posed an unacceptable risk to the community.

Witness Kyle Johnston said he was at a friend's house when he heard a loud bang and ran outside.

"I'm pretty shocked," he said.

"I don't know how to feel about this, it's not something you want to see."

Mr Johnston said other drivers in the area were shocked and "covering their faces".

'Very tragic events'

Assistant Commissioner Michael Corboy said the scooter was stationary when the pair was struck from behind.

"I can confirm that two male persons from Hurstville were killed in that crash," he said.

"Unfortunately the driver was thrown in the path of another vehicle and was killed instantly and the passenger died a short time later.

"We will be alleging that the bus driver was on his mobile phone as well as not wearing a seat belt at the time.

"They were both on the same scooter, I can't comment what company they were with but they appear to be food delivery people."

Two men from Hurstville were killed when their scooter was struck from behind. ( Supplied: Michael Akkari )

The bus driver was refused bail to appear in the Sutherland Local Court.

Five people died on the roads in New South Wales during the Australia Day long weekend.

A 17-month-old girl died after being struck by a four wheel drive in Lake Conjola, while two men died in separate crashes on Saturday.

Assistant Commissioner Corboy described the deaths as tragic.

"Operation safe return finished last night at midnight, unfortunately five people died on our roads over the safe return period — that was two more than the same period last year," he said.

"During that period we had a double fatal last night and also during that period unfortunately we had a toddler killed in a caravan park.

"Both very tragic events."