Champions McLaren discovered an electronics issue with Norris's car before it was due to head out on track.
Piastri's car was then pushed off the grid and back to the garage.
Mechanics removed the floor on Norris's car, with the team still working to resolve the problem as the grid closed for the second race of the season.
"It's an electric issue on the power unit, which I think was the same for Lando, but it's not the same electrical issue,'' Piastri told reporters shortly after Sunday's race start.
"They (the power units) are just incredibly complex, and there's so many rules on the power units that you sometimes change one thing and it has a very unintended consequence somewhere else.
"It's been a while since I've watched two grands prix on TV," added the Australian, who crashed out of the season-opener in Melbourne on his reconnaissance lap before the start of the race.
While Piastri's disappointing start to the season continues, Italian 19-year-old Antonelli celebrated the first win of his F1 career after besting championship-leading teammate George Russell in a Mercedes one-two in China from pole position.
Antonelli became the second-youngest race winner in the sport's history after four-time world champion Max Verstappen, who took his first victory in 2016 with Red Bull at just 18 years of age.
Ferrari's Lewis Hamilton finished a distant third in Shanghai, the seven-time world champion's first podium since he joined Ferrari last year, with teammate Charles Leclerc fourth after a lively battle between the two.
"Thank you everyone. Thank you so much. You made me achieve one of my dreams," said Antonelli over the radio after taking the chequered flag.
"I'm speechless. I'm about to cry to be honest," he said in his first interview as a winner in front of the Shanghai circuit crowd, before doing just that.
It was a nervous finish for the Italian, who locked up and went wide with three laps to go, cutting his lead over Russell to 7.4 seconds and finishing 5.515 clear.
It was Mercedes' second successive one-two in two races after Russell led Antonelli in the Australian opener last weekend.
"I gave myself a little bit of a heart attack towards the end with the flat spot (on his tyres)," said the first Italian winner since Giancarlo Fisichella for Renault in Malaysia in 2006.
"It was a good race."
Englishman Norris had qualified in sixth spot in Shanghai, with Piastri fifth, but both grid positions were left empty.
Piastri won in China last year from pole position, but the 24-year-old has made a horror start to 2026, crashing his McLaren on the way to the grid at the Australian GP in Melbourne last weekend.
It is the first time in more than 50 years that a Formula One driver has qualified but not started in consecutive grands prix. The last driver to suffer the same fate was New Zealander Bruce McLaren in the 1969 US and Mexican races.
The Williams of Alex Albon suffered a hydraulics problem on the way to the grid on Sunday, while Audi's Gabriel Bortoleto also failed to start, leaving 18 cars on the grid.
The Chinese race got under way just hours after Formula One announced next month's races in Bahrain and Saudi Arabia will not go ahead because of the war in the Middle East.
And MotoGP has postponed the Qatar race scheduled for next month until November because of the Middle East unrest.
