And the Spruce Goose is tiny by comparison? I think not.

"China has just taken the wraps off the world's largest amphibious plane. " Not quite, the 'Spruce Goose' H-4 is considerably larger, but no longer flying. Although the H-4 was strictly a seaplane, not amphibious, it may be of interest as a comparison.
General characteristics Crew: three Length: 218 ft 8 in (66.65 m) Wingspan: 320 ft 11 in (97.54 m) Height: 79 ft 4 in (24.18 m) Fuselage height: 30 ft (9.1 m) Empty weight: 250,000 lb (113,399 kg) Loaded weight: 400,000 lb (180,000 kg) Powerplant: 8 × Pratt & Whitney R-4360 Wasp Major radial engines, 3,000 hp (2,640 kW) each Propellers: four-bladed Hamilton Standard, prop, one per engine Propeller diameter: 17 ft 2 in (5.23 m) Performance Cruise speed: 250 mph (407.98 km/h) Range: 3,000 mi (4,800 km) Service ceiling: 20,900 ft (6,370 m)
More details here; https://en.wikipedia.org/wiki/Hughes_H-4_Hercules

"Forest fires and rescue?" Maybe instead to provide a supply link to their illegal islands until the airfields are completed.

I bet it would have trouble landing in the lakes in Alaska!

The Martin Mars is larger with about an 80 max take off weight and larger winspan.

Someone should tell the Chinese that this plane would be of enormous help with their building of airstrips and military outposts on the remote islands in the South China Sea, especially those near the Philippines, Indonesia or Vietnam...

7 yrs to build a 50 yr old Soviet plane is just sad. China still can't even make a decent jet engine even with all the design data for all of ours! And with their quality, I certainly wouldn't want to fly in it.

There aren't many examples of large amphibious airplanes being made these days anymore. You have to go back to the 1930's and 1940's when large planes such as these were being built to fly long range commercial routs. The question of why China is building this plane was revealed in the video. The development of this aircraft seems to be a part of China's strategic aims to extend it influence in the South China Sea. The "artificial islands" referred to are evidently those being built in disputed Philippine and Vietnamese waters.

No, the Spruce Goose was and is larger.

The h-4 Hercules (spruce goose) is considerably larger than this "world largest"