The NY Fed is publishing a weekly economic index (WEI) to track the behavior of the economy on a more frequent basis than GDP or the unemployment rate.  Here's a link to the article that describes the WEI.  While we have to wait until late April to get the first reading on first quarter GDP (and July for the second quarter), here's a chart showing WEI and economic growth (as well as some other measures of the macroeconomy) as of March 27:

What does the chart indicate in terms of economic growth given last week's WEI? Economic growth from March 2019 to March 2020 = -4%.  As you can tell, all of the decline took place in March 2020.  Given the way GDP is estimated, some of this will show up in the economic growth rate for Q1, but much of it will show up in Q2.