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We present new observations of C-band continuum emission and masers to assesshigh-mass ($>$8 $M_\odot$) star formation at early evolutionary phases in theinner 200 pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuumobservation is complete to free-free emission from stars above 10-11 $M_\odot$in 91% of the covered area. We identify 104 compact sources in the continuumemission, among which five are confirmed ultracompact H II regions, 12 arecandidates of ultra-compact H II regions, and the remaining 87 sources aremostly massive stars in clusters, field stars, evolved stars, pulsars,extragalactic sources, or of unknown nature that is to be investigated. Wedetect class II CH$_3$OH masers at 23 positions, among which six are newdetections. We confirm six known H$_2$CO masers in two high-mass star formingregions, and detect two new H$_2$CO masers toward the Sgr C cloud, making itthe ninth region in the Galaxy that contains masers of this type. In spite ofthese detections, we find that current high-mass star formation in the innerCMZ is only taking place in seven isolated clouds. The results suggest thatstar formation at early evolutionary phases in the CMZ is about 10 times lessefficient than expected by the dense gas star formation relation, which is inline with previous studies that focus on more evolved phases of star formation.This means that if there will be any impending, next burst of star formation inthe CMZ, it has not yet begun.

A Census of Early Phase High-Mass Star Formation in the Central Molecular Zone