The pledges China and the US made to keep prospects alive for a comprehensive trade deal did little to alter the deteriorating growth outlooks for both countries because they were sealed with something economists don't trust: a handshake.

China agreed Friday to more than double its annual purchases of American agricultural products to as much as $50bn (R740bn) - providing a political shot in the arm to a rural constituency that's key to President Donald Trump's 2020 re-election bid more than a meaningful lift to a nation with gross domestic product of about $21trn (R310trn).

Trump tweeted Sunday evening that China has begun making agricultural purchases, echoing comments he made Friday in the Oval office.

In return, Beijing convinced the US to holster another tariff increase set for this week as White House officials worry about slower growth at home.

Left on the table, though, was Trump's biggest economic threat yet and the darkest cloud in the outlook: import taxes on all remaining Chinese shipments due to start December 15 that would make a range of popular consumer products more expensive.

"We have a lot of work to do, but I am confident that both sides are going to work very hard and anticipate we will be closing this," Treasury Secretary Steven Mnuchin said Sunday on the ABC News programme .

WATCH: Clouds gather ahead of US-China trade talks

Investors are more wary. Though US equities rose last week as trade tensions eased, they trimmed gains Friday afternoon when reality set in. The deal Trump called the biggest "in the history of our Country" had a significant shortcoming: it wasn't a signed document yet, even though it has, in effect, been on the table for more than a year.

So economists reacted with a range of scepticism and doubt about what it means for growth projections that are coming down as the 18-month trade war drags on.

"There is not yet a viable path to existing tariffs declining, and tariff escalation remains a meaningful risk," Morgan Stanley strategists Michael Zezas and Meredith Pickett wrote on Friday. "Thus, we do not yet expect a meaningful rebound in corporate behaviour that would drive global growth expectations higher."

Raymond Yeung, chief Greater China economist at Australia & New Zealand Banking Group, said that despite the latest progress, tensions are unlikely to ease soon and the economic risks will linger as talks move through various stages.

'High hurdles'

"The Phase I agreement mainly covers agricultural purchases, tariff suspension, and market access," Yeung wrote in a research note Saturday with ANZ colleagues Betty Rui Wang and Zhaopeng Xing. "But core issues of technology transfer and national security still face high hurdles before a resolution in our view."

What economists say

"Past experience is that US-China trade agreements aren't worth the paper they are written on, and this one hasn't even been written down. For now, though, indications on trade are a little more positive. If that persists, it could help put a floor under sliding global growth."

Chinese GDP data for the third quarter, slated for release Friday, is expected to show that output growth in the three months to September eased to 6.1%, the slowest in almost three decades. That pace would be barely enough to allow the Communist Party to claim it's hitting its long-term growth targets.

For economists to get more optimistic about the outlook, Washington and Beijing between now and the November leaders' meeting of the Asia-Pacific Economic Cooperation forum will have to make more progress on thornier trade issues such as enforcement and intellectual-property protections.

"Until such evidence is available, we must conclude that this pause is more 'uncertain' than 'durable,'" the Morgan Stanley strategists wrote.